On June 3,1946, Assumption welcomed Father Michael Hinnebusch as its third pastor. Prior to this assignment, he had served four years as chaplain in the United States Army. Father Hinnebusch is remembered for many accomplishments, not the least of which is the final settlement of the parish debt in 1951. He did this through a number of Parish Development Day drives that raised most of the needed revenue. The country was coming out of difficult financial times, and the parish continued to grow, numbering 1,612 families.

Along with the parish Church Committee, Father Hinnebusch decided to continue the original program set up by his predecessors for the completion of the church interior. He worked closely with the architect, Leo McMullen, to add the finishing touches to the interior. This included the installation of two marble side altars, four marble statues, the baptistery, and the installation of 32 stained glass windows, 16 clerestory windows, and the rose window in the choir loft. In 1964, Fr. Hinnebusch authorized the purchase of a beautiful Casavant-Freres Limitee pipe organ, which remains one of the finest in the city.

In addition, the growing school enrollment required the addition of six new classrooms and a new furnace. The parish acquired property on North Jackson Avenue on which to build a new rectory. The Sprague Avenue convent was linked to the former rectory building, thus providing adequate facilities for the 17 Sisters who staffed Assumption School. Perhaps Father Hinnebusch's most ambitious undertaking was the erection of the "new school" building on Florence Avenue in 1959. The building was needed to accommodate the more than 1,000 students enrolled by that time.

On November 1, 1951, the dogma of the Assumption of the Blessed Virgin Mary was proclaimed by the Catholic Church. This event was particularly significant to Assumption parish, which had worshiped under this title since its foundation. The progress of the parish, both financial and spiritual, during Father Hinnebusch's 21-year pastorate, speaks to the deep faith and steadfastness of the congregation. It took many sacrifices, great and small, financial and personal, to bring Assumption to its present glory.

Father Hinnebusch retired from active ministry in 1967.