During that time, Ellwanger became colleagues with Martin Luther King Jr. Ellwanger answered the call of King and the Southern Christian Leadership Conference to recruit students and clergy to join the movement in Selma to take part in the march for voting rights from Selma to the state capital of Montgomery.

Ellwanger took part in mass meetings, involving himself and members of his congregation in Civil Rights activities, and ultimately took a leadership role in community organizing.

[4] Ellwanger spoke at the funeral for one of the four girls killed in the 16th Street Baptist Church bombing in September, 1963, where Dr. King delivered the eulogy.

[10][11] After retiring from Cross Lutheran, Ellwanger spent a decade as a grassroots organizer for WISDOM, a statewide coalition of social justice groups in Wisconsin.

[13] Ellwanger has been a subject in a number of books, including King: A Biography by David Levering Lewis, Eyes on the Prize: America's Civil Rights Years, 1954-1965 by Juan Williams, Kids in Birmingham 1963, and On the Road to Freedom: A Guided Tour of the Civil Rights Trail by Charles E. Cobb Jr.