The Cathedral of Christ the King is a most impressive building visible from every approach road to Mullingar. Its twin towers, which are one hundred and seventy six feet in height, surmounted by gilt bronze crosses, are dominant features in the landscape. The Cathedral is well situated on high ground near the center of the town. It is part of a religious complex, which was gradually built up during the nineteenth century, on what was originally the back of the town. Catholic churches were rarely built in the nineteenth century in prominent positions due to restrictions on Catholic land ownership. This religious complex is reflected in the name of the street, which runs at right angles to the Cathedral – Bishopsgate Street.

Entering the grounds of the Cathedral from Mary's Street through its impressive entrance gates, much of this complex is clearly visible. On the left of the Cathedral lies St. Mary's College, a primary and a secondary school. On the right are the Presentation primary schools, begun in 1825. Directly to the back and right of the Cathedral lies Cathedral House, the former Episcopal palace and now the parochial house, which was built during the episcopacy of Bishop Thomas Nulty in 1873. The second entrance to the Cathedral grounds, which comes directly off Bishopsgate Street, is known as the Old Cathedral Gates because it served as the entrance to the old Cathedral that was demolished in 1936 to make way for the present one. Directly to the right of these gates lies the parish community centre. It was here, that Bishop John Cantwell was consecrated in 1830, in what was then the parish chapel of Mullingar, a much smaller structure than the present building.

  In the grounds, between the Cathedral and the community centre, the more recent bishops of Meath are buried in the grounds. The first bishop buried here was Bishop Laurence Gaughran (1906-1928). The others interred here are Bishop Thomas Mulvany (1929-1946), Bishop John Kyne (1947-1966), Bishop John McCormack (1968-1992), Bishop Thomas Nulty (1866-1898) and Bishop Matthew Gaffney (1898-1906). Bishop Nulty was re-buried in the grounds in 1989. Originally he had lain in the crypt of the Old Cathedral along with Bishop John Cantwell (1830-1866). When the new Cathedral was built it did not prove possible to move the remains of Dr. Cantwell, but those of Dr. Nulty were repositioned under the new structure. As a formal crypt was never laid out in the new Cathedral, it was decided to re-inter Dr. Nulty in the grounds as part of the jubilee celebrations for the Cathedral in 1989. Bishop Gaffney was buried originally in the Franciscan Abbey in Multyfarnham. On 2 November 2009, one hundred years after his death, his remains were re-interred beside the grave of Dr. Nulty. A prominent feature close to the Episcopal graves is a large crucifix, which was erected to commemorate various nineteenth century parish missions, the first of which was held in 1856.

  In 1997, part of the religious heritage of the town and parish was uncovered. In order to facilitate a modern development, archaeologists excavated a site at Austin Friars Street close to the old Augustinian monastery in the town. The remains of a number of Augustinian monks were discovered. Some of the bodies were decorated with scallop shells, which indicated that during their lifetime they had completed a pilgrimage to the shrine of St. James at Compestella in Spain. A number of these remains were re-interred in the lawn opposite the entrance doors of the Cathedral in August

The Cathedral of Christ the King is Basilican in form with twin towers and a dome. The style is Renaissance based on the Roman Doric order. It is faced entirely with chiseled stone, largely of granite from Barnacullia, Co. Dublin, while the dressings are of limestone from quarries at Stradbally, Co. Laois, Navan, Co. Meath and Mountnugent, Co. Cavan. The upper part of the towers is built entirely of limestone and the drum of the dome in granite. Behind the facing lies the structure of the building, which is composed of Glasgow steel and brickwork from Dolphin's Barn brickwork, Dublin.

 Along with the towers, the most striking feature of the front of the building is the Tympanum over the main entrance. Here in the pediment, which is about forty-two feet long and nine feet high to the apex, is an exquisite sculpture, the work of Albert Power. R.H.A., executed in Portland stone. It represents Our Lady with cherubim bearing as an offering to her Son, Christ the King, a model of the old Cathedral of the Immaculate Conception. On her left are the figures of St. Peter and St. Patrick. On the right are the figures of Pope Pius XI, (at whose request the Cathedral was dedicated to Christ the King), Thomas Mulvany, the bishop of Meath at the time, and the Primate of All Ireland, Cardinal Joseph Mac Rory.

 To the right and left of the main entrance door of the Cathedral are four sculpted panels, representing from left to right, the Papal coat of arms, Abraham offering his son in sacrifice, Melchizedek offering sacrifice, and finally the coat of arms of the diocese of Meath. Over the main entrance door is a sculpture representing the head of Moses. On either side of the Cathedral, the windows have carved reliefs representing ten of the apostles. Henry Thompson of Dublin sculpted all these works.

 Directly under the pediment is a Latin inscription - ‘D N Jesu Christo Regi haec Cathedralis Ecclesia dedicata est A.D. 1936’ - which states that the Cathedral was dedicated to Christ the King in 1936. The Cathedral clock is located in the east tower. Originally installed in the old Cathedral by Gillet and Johnson & Co of Croydon, England in the 1880s, it was modified by them for use in the new Cathedral, and given a new clock face. It continued in use as a manual operation until its automation in the 1990s. The Angelus bell is hung in the west tower and was recast for the new Cathedral.

 The Cathedral nave is one hundred and twenty feet long and fifty feet wide, and with the aisles seats about 1,600 people. From this perspective the eye is carried directly to the sanctuary, and in particular to the mosaic of the Ascension in the Apse and to the High Altar. Over the sanctuary is a large domed stain glass light, which lies directly under the dome of the Cathedral. Beneath this light are four carvings representing the four evangelists. The ceiling of the nave, about fifty feet above the floor, is coffered, with the openings in the sides of the coffer beams providing both decoration but also ventilation.  The columns are coupled by a full entablature, alternating with an arch that spans the wider spacing. They are made of Rochambeau marble, with caps of 'Irish White' marble, which has in fact a delicate green tone. The radiators between the columns are encased in black and coloured marble with bronze grills, which render them not only inconspicuous but also blend with the architectural character of the building.

The Stations of the Cross are located between the columned arches. These have been described as the most successful of their type in this country. Excellent examples of opus sectile work, i.e. crafted out of small pieces of coloured tile, the figures are rendered distinct not only by a judicious blend of colours but also by an outline of gold mosaic. Consequently their meaning can be easily and clearly interpreted.

  On either side of the nave, between the two rows of coupled columns is an aisle ten feet wide. The aisles have barrel-vaulted ceilings between the coupled columns and groined vaulting over the intervening spaces. The walkways between the aisles and the side walls are five feet wide and have barrel vaulted ceilings, alternating with flat treatment. The vaulted ceilings are complimented by attractive bronze light fittings. Along the side walls of the Cathedral can be seen the candles and crosses which were installed for the consecration in 1939. In each of the transepts are two side chapels; on the left side chapels dedicated to St. Therese and St. Anne; and on the right side chapels dedicated to St. Joseph and St. Patrick. Each of the aisles also terminates in a chapel, that on the right being dedicated to the Blessed Sacrament and that on the left named the Lady Chapel. To the left of the Lady chapel is the former mortuary chapel, now used as a perpetual adoration chapel. All the windows in the Cathedral are made of a very special type of slab glass of a cream tint, which gives a hint of actual liquid colour. The large windows in the transepts have also rich multi-coloured pot metal stain glass borders.

 The seats in the centre aisles are of Austrian oak, as are the confessionals and the sanctuary stalls. The confessionals were specially designed to fit into the wall recesses and their carving and golden timber grills make them especially attractive. The seats in the side aisles are copies of the centre aisle seats. They are made of Irish oak, and were installed in the 1960s. The central passage of the nave, the side ambulatories and the cross passages of the Cathedral are paved in mosaic. Elsewhere in the Cathedral, oak and mahogany wood block flooring is laid. The doors of the Cathedral are of mahogany and each of the entrances has an attractive bronze holy water font. During the renovation of the heating system in 1996 extra radiators were provided but these are very cleverly disguised in front and rear of the rows of seating.

 The sanctuary is separated from the main body of the Cathedral by the altar rails. These are in white marble, relieved on the piers by Persian and Chilean Lapis Lazuli panels outlined in gold mosaic. The sanctuary has a depth of seventy-four feet and has a minimum width of thirty-four feet. Three very beautiful bronze sanctuary lamps hang from the ceiling above it. The centre lamp, hexagon in shape, is a particularly fine piece of bronze artistry. It is richly carved and chased and has the figure of Christ the King sculpted on its front and back. The two side lamps are a pair and are also hexagon in shape. They are made of burnished bronze, and have coronas and acanthus leaves in high relief. The lamp on the left hand side was the gift of the Westmeath Men's Association in New York.

  The sanctuary of the Cathedral was remodelled in 1984 in accordance with the liturgical changes, which emerged from the Second Vatican Council. This was planned however, in a way sensitive to the original design. The sanctuary floor was not disturbed, even though this left the altar at a considerable distance from the congregation. A new ambo and celebrant's chair were installed in the sanctuary near the altar rails on the left and right hand sides. These were crafted from a blend of either the same or similar marbles, which were originally used in the High Altar. The table of the High Altar was separated from the reredos and the number of steps leading to it was reduced from five to three. Supplies of the same marbles as the originals were procured in order to face the newly exposed front of the reredos. The only other change effected was the remodelling and relocation of the Bishop's chair, made necessary by the introduction of the new ambo.

 The sanctuary floor is mainly cruciform in shape and is outlined in rich Brocatello Siena, Levanto, and Rose Aurore marbles, along with red marble from the Castletown quarries in Co. Kerry. Every attempt was made in the decoration of the Cathedral to include Irish marble wherever possible. The floor as seen from the altar rails has an enamelled mosaic panel of adoring angels incensing with golden thuribles just in front of the sanctuary gates. There are four circular enamelled mosaic panels representing clockwise from bottom left, Blessed (Now Saint) Oliver Plunkett, St. Finian, St. Columcille and St. Colman, all saints with close connections to the diocese. In the centre of the sanctuary floor is a rectangular border of Connemara marble, enclosing a circle of red marble from Kerry that has the shape of a cross very cleverly outlined at the centre. On left and right of the sanctuary are beautifully carved oak stalls.

The pilasters in the sanctuary are a departure from the Rochambeau columns of the nave. The front four pilasters are panelled in Moroccan onyx and margined in Paonazzo with a fine gold mosaic inlay. The angles are protected by munse metal strips, which have a spiral pattern. The caps and bases are of 'Irish White' marble, which is a delicate green, in keeping with the nave columns. The six pilasters and two half pilasters in the rear of the sanctuary are panelled in Swiss Cipollino marble and are margined with Paonazzo. They have the same munse metal strips as the front pilasters but are without the gold mosaic inlay. Not enough Moroccan Onxy could be obtained to panel all the sanctuary pilasters, hence the different marbles used.

 The altar is at once very simple but very beautiful. Originally, it was to have a richly ornamented Baldachino but this was not proceeded with. It consists of a table, reredos and Tabernacle. It is outlined in white marble, the three steps being Lamantine. The reredos has a nine-foot bronze Crucifix and seven equally impressive candelabras. Attached to this reredos is the Tabernacle. Its dome is based on the design of an inverted shell, surmounted by the globe and cross. The Tabernacle door is quite unique, the metal being carved, not engraved, coated with twenty-two carat gold and ornamented with amethysts in a pure Celtic design.

 On the altar table there are depicted two groups in white marble representing the sacrifice of Noah and that of Abel. The right hand one is particularly interesting, because it shows the hand of God accepting the sacrifice of Abel, while the sacrifice of Cain is shown as unacceptable, as the flames of the sacrifice are thrown downwards towards the earth, because Cain was a murderer in his heart. The central panel of the altar is made of Mexican onyx with jasper markings, surrounded by a carved framework, with a bronze cross as the central emblem. Other marbles used in the decoration are Brocatello Siena, and red coloured marble from France.

 Directly above the altar, in the apse, is a magnificent mosaic of the Ascension. Completed in 1939, in time for the consecration of the Cathedral, it is composed of nineteen figures and six cherub angels. The figure of Christ is crowned by two angels and is accompanied by two others. On the ground along with two further angels are depicted Our Lady, St. Peter with the Keys and the other eleven disciples. The Latin inscription at the base of the work -Regnum meum non est de hoc mundo, are from the words of Christ addressed to Pontius Pilate, My kingdom is not of this world. (Jn 18:36). The inscription is on white marble moulding, while the lower walls are lined with Paonazzo, Brocatello Siena, Moroccan onyx and a dark marble surbase. Beneath the apse is a small altar, called a robing altar that in the past was used for the celebration of private masses.

 The entrance to the Pulpit is directly opposite the Blessed Sacrament chapel. Designed as a sermon in stone, the body of the Pulpit consists of large carved groups in pure white marble with inlaid borders of rich green Connemara marble, surrounded by gold mosaic borders. Directly opposite St. Therese’s chapel is the baptismal font. This was relocated here in 1997 from the Baptistry in order to facilitate its use for the new rite of baptism. It consists of two solid bowls of Carrara marble, both of which are resting on a solid central column of Connemara marble. The large bowl has also other slender Corinthian columns of Sienna and Brocattelo marbles. The reliefs representing the four evangelists are carved from the same slab of marble as the bowl.