The figures most closely associated with construction of the Cathedral of the Immaculate Conception were Bishop Nicholas Matz, Father Hugh L. McMenamin ("Father Mac"), and millionaire parishioner John K. Mullen. The site chosen form the Cathedral of the Immaculate Conception was in the most affluent Denver neighborhood at the time and on one of Denver's most prestigious streets. Hugh L. McMenamin (1872-1947) made completion of the Cathedral of the Immaculate Conception a reality in 1912 through aggressive fundraising and careful planning. A parade of 20,000 people traveled on Broadway and up E. Colfax Avenue to the new Cathedral for the dedication. Father McMenamin became a monsignor in 1933.
ON 7 August 1912, the west spire of the cathedral was hit by lighting. Eighty-five years later, on 23 June 1997, the east spire was hit by lightning. Both jolts from above required extensive renovation. The building also had a sensitive interior renovation 1974. In 1979, in recognition of its architecture and history, Pope John Paul II elevated Immaculate Conception Cathedral to a minor basilica.
Leon Coquard, a Detroit architect, designed the Cathedral in the French Gothic Style. The design was said to be similar to the one in Bishop Matz's home of Munster, France. When Conquard became ill, Denver architects Aaron Gove and Thomas Walsh took over supervision of the construction.