Berresford "Berry" Bingham, 64, an official with Service Employees International Union Local 1021, was found in his home in the 500 block of Henry Street, near the West Oakland BART station, at about 11:35 a.m. on Tuesday, Officer Holly Joshi said.
Officers found Bingham after responding to a request that they check on his well-being, Joshi said.
An autopsy is being conducted Wednesday to determine the cause of his death, Joshi said.
Local 1021 Director Bill Steck said Bingham had been with the union for about 16 years.
Steck said Bingham advocated for Alameda County employees and home health care workers for many years and most recently served as a coordinator working with churches and community and social justice groups.
Bingham's work took him to cities throughout Northern California, including Stockton, where he had been working on a Head Start campaign, Steck said.
Bingham "had an incredible commitment to helping low-wage workers and home health care workers," Steck said.
One of the things Bingham was proudest of was arranging for then-Sen. Barack Obama to work as a home health care worker in Oakland for a day in August 2007 when he was beginning his presidential campaign, Steck said.
The work was part of the SEIU's "Walk a Day in My Shoes" program in which they asked candidates seeking their endorsement to spend a day as a worker.
The SEIU ultimately endorsed Obama on Feb. 15, 2008.
Steck said several SEIU employees went to Bingham's home on Tuesday because he hadn't been heard from for several days.
Bingham is survived by three children, Steck said.
He said Bingham was a deacon at his church.