A. Cornelius Baker, who spent nearly 40 years working with urgency and compassion to improve the lives of people with H.I.V. and AIDS by promoting testing, securing federal funding for research and pushing for a vaccine, died on Nov. 8 at his home in Washington. He was 63.

Gregory Nevins, his companion, said the cause was hypertensive atherosclerotic cardiovascular disease.

Mr. Baker — who was gay and who tested positive for H.I.V. — became active in Washington in the 1980s, during the early years of the AIDS epidemic. He soon distinguished himself as an eloquent voice for people with H.I.V. and AIDS. A policy wonk and health-care expert, he held positions in the federal government and with nonprofits, including serving as the head of a clinic for the L.G.B.T.Q. community.

“He was very kind, very embracing and inclusive — his circles, both professionally and personal, were the most diverse I’ve ever seen, which was driven by his Christian values,” said Douglas M. Brooks, a director of the Office of National AIDS Policy during the Obama administration. “His ferocity appeared when people were marginalized, othered or forgotten.”

In 1995, as the executive director of the National Association of People with AIDS, he helped establish June 27 as National H.I.V. Testing Day. “This effort was designed to help reduce the stigma of H.I.V. testing and to normalize it as a component of regular health screening,” Mr. Baker wrote in 2012 on the website of FHI 360, a global health organization for which he served as technical adviser.

As an adviser to the National Black Gay Men’s Advocacy Coalition from 2006 to 2014, Mr. Baker worked with the Centers for Disease Control and Prevention and the National Institutes of Health to help fund research for the care of gay Black men with H.I.V. and AIDS.