Michael Schwartz, a conservative activist who served as chief of staff to Tom Coburn (R.-Okla.) in the U.S. House of Representatives and U.S. Senate, died Feb. 3 at his home in Germantown. He was 63.

The cause was amyotrophic lateral sclerosis, also known as Lou Gehrig’s disease. A son, Joseph Schwartz, confirmed the death.

Mr. Schwartz spent his early career in public affairs with the Catholic League for Religious and Civil Rights in Milwaukee. He settled in the Washington area in 1986 and worked over the years with conservative lobbying groups including the Free Congress Foundation and Concerned Women for America.

Mr. Schwartz worked for Coburn in the House from 1995 to 2000 and in the Senate from 2004 to 2012.

At conservative gatherings, the aide sometimes drew wider public attention for making harsh remarks about gays and calling for a “mass impeachment” of what he described as activist federal judges. The latter prompted Coburn to issue a statement distancing himself from the remark.

After Mr. Schwartz’s death, the senator said in a statement that his former chief of staff was “an extraordinary servant and faithful leader [who] showed everyone — by his life, deeds and words — that things that are unseen are the things that matter.”

Mr. Schwartz was born Michael Duffy in Philadelphia on July 16, 1949, and later took the surname of his adoptive stepfather.

His home life as a child was difficult, he once said, but Catholic school instilled in him a sense of discipline and purpose that had a defining effect on his career in conservative activism and politics, notably his support for government-financed school vouchers.

“My own family had all the social pathologies — drug abuse, welfare dependency, illegitimacy — and I’ve seen how public policy makes it more difficult,” he told the publication National Journal in 1996.

He was a 1972 graduate of the University of Dallas. He spent a period as an organizer for the antiabortion rights group Operation Rescue before joining the Free Congress Foundation, founded by Republican strategist Paul M. Weyrich. Mr. Schwartz was an early figure in the foundation’s efforts to launch a conservative satellite TV network called National Empowerment Television in the early 1990s.

Mr. Schwartz’s books included “The Persistent Prejudice: Anti-Catholicism in America” (1984). In interviews and commentary, he often criticized what he deemed the church’s weak institutional handling of crises, including anti-Catholic literature and other forms of hatred.

Up to a point, Mr. Schwartz warned against blaming the news media for the quantity of coverage of the church’s sex-abuse scandal, which involved the great efforts some church leaders made to shield the offending priests. But Mr. Schwartz also pointed out what he considered excesses by tabloids and some liberal columnists for a sweeping condemnation of Catholicism.

“These errors seem to reflect sloppy journalism rather than deliberate bias,” he wrote in Insight magazine in 2002. “In general, the tone of most coverage of the scandals was fairly restrained and sympathetic to the great majority of Catholic laity and clergy, who were as appalled as everyone else by the terrible revelations.”

He was a lector at Mother Seton Parish in Germantown and a past director of its program to bring adults into the Catholic Church.

Shortly before his death, he received awards from the National Pro-Life Religious Council and the Catholic lay group Legatus.

Survivors include his wife of 41 years, Rose Ann Guidry Schwartz of Germantown; four children, Brian Schwartz of Kenosha, Wis., Joseph Schwartz of Havertown, Pa., Elizabeth Needleman of Chicago and John Schwartz of Germantown; his mother, Helen Duffy of Homosassa Springs, Fla.; a brother; a sister; and seven grandchildren.