The cathedral church is built of reinforced concrete and steel, with an exterior facade of Indiana limestone. The interior of the church, which seats 950 people, has 19,000 square feet of terrazzo flooring. The church's is 157 feet in diameter, and its main aisle runs 88 feet from the glass doors to the altar.

The cathedral's ceiling, at a height of 72 feet, is made of Douglas fir and is supported by sixteen laminated wood beams that are about 60 feet long. The beams meet at a steel ring, in the center, that is about nine feet in diameter. The ring creates an oculus, from which the spire rises to a height of 29 feet. The outer roof is made of copper, with sixteen gables in a design which signifies a crown.

Within the Cathedral, there are twelve pillars covered in walnut symbolizing the twelve Apostles. Consecration candles for each pillar were added in 2009 by Bishop John R. Gaydos.

Sound and surface noise inherent in terrazzo flooring required unusual attention to achieve good acoustics in the large open, room. Padded walls, covered in mesh, with strips of walnut help to absorb the noise. Other acoustical features include the padded pews, as well as the decorative faceted glass windows. One interesting feature of the design of this Cathedral is that there are no supporting pillars in the open expanse.

The sanctuary wall is polished buff travertine. The steps and raised surfaces in the sanctuary are made up of contrasting walnut travertine.

The altar is a single block of polished marble weighing 7000 pounds. Within the altar are relics from St. Clement, St. Irenaeus, and St. Aurelius.

The sanctuary itself is oval-shaped and was designed in a post-Vatican II style, for ceremonies in which the bishop presides. The cathedra, or bishop's throne, sits immediately beneath the bishop's coat of arms, which hangs on the sanctuary wall.

The crucifix with a corpus of walnut travertine is suspended from the wall. The corpus is 5 feet tall and weighs over 450 pounds.

During the Christmas season, the Cathedral is noted for its Nativity set, which was first displayed in 2009.

The Blessed Sacrament Chapel is immediately to the left of the sanctuary. The chapel seats 50, and a glass partition separates it from the rest of the main seating area.

Within the altar of the chapel are relics from St. Clement, St. Irenaeus, and St. Liberatus.

Five faceted glass windows in the chapel, created by Jacoby Studios in St. Louis, symbolize the functions of the priest. These windows are visible from the main seating area in the cathedral.

The first window pictures the carpenter's hammer and square associated with St. Joseph, patron of priests.

The second window shows the Greek symbols Chi-Rho, with rings and leaves indicating a priest's role in performing Christian marriages.

The third window with a scroll and lamp illustrate a priest's service as teacher.

The fourth window pictures a shepherd's crook and book, alluding to the pastoral duties and to promulgating the Gospels.

The fifth window, which is in the sanctuary of the chapel, shows crossed branches, a crown, and a star as reminders of eternal reward in victory over death, and the priest's function in performing Christian burial.

Also, within the chapel is a cross, known as the Jubilee Cross, which contains a relic of the True Cross. The cross was created by Lage's Cabinet Shop of Jefferson City for the Jubilee Year of 2000.

As was ancient custom, the sacristy is at the entrance of the Cathedral, permitting processions to and from the altar.

The Bishop's private sacristy was installed in 2005 immediately adjacent to the main sacristy. There is a minor sacristy attached to the Blessed Sacrament Chapel.

The baptistry is also located at the entrance, remodeled as recently as 2006.

Two skylights in the ceiling bathe the font in natural light.

The font is the original Italian marble baptistry made for the Cathedral.

The floor is made of similar marble to that which is in the sanctuary.

An ambry, built in 2004, resides in the baptistry and is made of wood and glass. It contains the oil of the sick, Sacred Chrism, and the oil of the Catechumens, blessed at the Chrism Mass, which is celebrated each Lent in the Cathedral.

A statue of the Risen Christ is also present in the Baptistry.

The Cathedral features an undercroft, which serves as a large multi-purpose room for various parish and diocesan functions. The undercroft can be accessed directly from the Cathedral Proper, or by doors which open to the south.

The main doors of the cathedral weigh an incredible 500 pounds each. Due sloping grounds, these doors stand at ground level. Decorative embellishments to the light-finished wooden doors are a reminder of Christ.

The doors were designed by Brother Stephen Erspammer, S.M., of St. Louis. The right and left sets of doors have handles in the shape of a Greek Alpha and Omega, recalling John's beatific vision of Christ in Revelation.

A bronze medallion embedded in the center set of doors depicts an eternal Christ, seated among the sun, moon, stars, and rainbows of the heavens. With one hand, the figure makes the ancient gesture of a teacher.

The other hand holds the book of Scriptures, with the words "Ego sum lux mundi," which means "I am the light of the world."

The Christ image is situated on one side of the medallion, so that it remains whole, even when the Cathedral doors are open.

The style is in keeping with ancient Church art and the contemporary design of the Cathedral.  The doors were commissioned and blessed by Bishop Gaydos. The blessing took place in June 2001 on Pentecost Sunday. On a practical note, one set of doors does have an electronic device that enables those with disabilities to open the door, making the Cathedral accessible for many.

The twelve triangular stained glass windows in the nave of the cathedral employ their symbolism in color and light.

As one moves from the sanctuary, on either side, the color in the windows grows proportionately lighter to surround a figure of the Risen Christ over the doors of the cathedral.

Marble figures of St. Joseph and of the Blessed Virgin Mary stand in wall niches in the Cathedral.

A figure of the Sacred Heart of Jesus stands at the Blessed Sacrament Chapel to the left of the nave. Each of these figures is five feet tall and is made of unpolished travertine.

The sculptors' tool marks are still visible in the figures. There are fourteen polished marble Stations of the Cross hanging around the seating area. There are three mosaics—the Infant Jesus of Prague, Our Lady of Perpetual Help, and St. Anne.

The statuary, mosaics, and stations were imported from Italy for the Cathedral.