Ahmann worked in Chicago for several years as director of the Chicago Catholic Interracial Council.
In 1960, he founded and became the executive director of the National Catholic Council for Interracial Justice.
As director, Ahmann organized the National Conference on Religion and Race, the first national meeting on civil rights between Catholic, Protestant, and Jewish leaders.
The conference was held at the Edgewater Beach Hotel in Chicago on January 14–17, 1963.
Ahmann scheduled it to coincide with the Emancipation Proclamation's 100th anniversary.
Ahmann said his goal for the conference was to:
examine the role of religious institutions in race relations and then move on to propose and inspire renewed action and interreligious projects to increase the leadership of religion in ending racial discrimination.

Leaders from 78 denominations attended, and speakers included Martin Luther King Jr., Sargent Shriver, and Abraham Joshua Heschel.
One attendee said it was an achievement in itself that Protestant, Catholic Jewish and Orthodox leaders had even come together: "A total of 1,000 delegates — about 750 official delegates and 250 observer delegates" attended.
After Ahmann's speech, Heschel invited Ahmann to the stage and said, "We are here because of the faith of a 33-year-old Catholic layman."
Heschel kissed Ahmann on the head, and Ahmann received a standing ovation.
A journalist who attended concluded that even if the attendees did nothing after they left the conference, they would never be the same.
He also explained that after the conference it was expected that committees of the three religions would form on local and regional levels but in order to be successful they needed to be more unanimous in action, not independent.

Ahmann was asked by organizers of the 1963 March on Washington for Jobs and Freedom to find a Catholic bishop who would serve as a Catholic chairman for the march.
Unable to find a willing bishop, Ahmann himself volunteered to join the organizing committee and make a speech at the march.
Ahmann, as the Catholic presence, along with white leaders Walter Reuther, Eugene Carson Blake, and Joachim Prinz, joined the original "Big Six" to organize the march as the "Big Ten."

At the August 28 March on Washington, Ahmann gave a speech on the steps of the Lincoln Memorial.
He asked:
Who can call himself a man, and take part in a system of segregation which frightens the white man into denying what he knows to be right, into denying the law of his God?

Ahmann's speech preceded King's "I Have a Dream" speech.

In 1965, Ahmann urged all United States diocese clergy to attend the Selma to Montgomery marches, in response to King's call for participation.
In the same year, he gave the commencement speech at the College of Saint Benedict, where he encouraged women to fight for rights.
In 1967, Ahmann wrote a letter to the incarcerated King, saying, "Our conference sends you greetings while you serve sentence for your witness for humanity, dignity and justice."
The King Center has uploaded this telegram to their online archives for the public to view.

Ahmann continued to show his support to King and the movement in 1967 when he sent him a telegram on the 10-year anniversary of the Southern Christian Leadership Conference to congratulate them on all of the work they had done and continued to do for human rights.
Ahmann worked in Chicago for several years as director of the Chicago Catholic Interracial Council. In 1960, he founded and became the executive director of the National Catholic Council for Interracial Justice. As director, Ahmann organized the National Conference on Religion and Race, the first national meeting on civil rights between Catholic, Protestant, and Jewish leaders. The conference was held at the Edgewater Beach Hotel in Chicago on January 14–17, 1963. Ahmann scheduled it to coincide with the Emancipation Proclamation's 100th anniversary. Ahmann said his goal for the conference was to:
examine the role of religious institutions in race relations and then move on to propose and inspire renewed action and interreligious projects to increase the leadership of religion in ending racial discrimination.
Leaders from 78 denominations attended, and speakers included Martin Luther King Jr., Sargent Shriver, and Abraham Joshua Heschel. One attendee said it was an achievement in itself that Protestant, Catholic Jewish and Orthodox leaders had even come together: "A total of 1,000 delegates — about 750 official delegates and 250 observer delegates" attended. After Ahmann's speech, Heschel invited Ahmann to the stage and said, "We are here because of the faith of a 33-year-old Catholic layman." Heschel kissed Ahmann on the head, and Ahmann received a standing ovation. A journalist who attended concluded that even if the attendees did nothing after they left the conference, they would never be the same. He also explained that after the conference it was expected that committees of the three religions would form on local and regional levels but in order to be successful they needed to be more unanimous in action, not independent.
Ahmann was asked by organizers of the 1963 March on Washington for Jobs and Freedom to find a Catholic bishop who would serve as a Catholic chairman for the march. Unable to find a willing bishop, Ahmann himself volunteered to join the organizing committee and make a speech at the march. Ahmann, as the Catholic presence, along with white leaders Walter Reuther, Eugene Carson Blake, and Joachim Prinz, joined the original "Big Six" to organize the march as the "Big Ten."
At the August 28 March on Washington, Ahmann gave a speech on the steps of the Lincoln Memorial. He asked:
Who can call himself a man, and take part in a system of segregation which frightens the white man into denying what he knows to be right, into denying the law of his God? 
Ahmann's speech preceded King's "I Have a Dream" speech.
In 1965, Ahmann urged all United States diocese clergy to attend the Selma to Montgomery marches, in response to King's call for participation. In the same year, he gave the commencement speech at the College of Saint Benedict, where he encouraged women to fight for rights. In 1967, Ahmann wrote a letter to the incarcerated King, saying, "Our conference sends you greetings while you serve sentence for your witness for humanity, dignity and justice." The King Center has uploaded this telegram to their online archives for the public to view.
Ahmann continued to show his support to King and the movement in 1967 when he sent him a telegram on the 10-year anniversary of the Southern Christian Leadership Conference to congratulate them on all of the work they had done and continued to do for human rights.
Mathew Ahmann