Kluwe, 31, was signed Wednesday, and the official announcement will be made Thursday by the Raiders. He was released by the Minnesota Vikings May 6, and replaces punter Shane Lechler, who left Oakland via free agency for the Houston Texans, Fox Sports reported.
Kluwe, a UCLA graduate in political science and history, is a vocal advocate of equality, in sports and in life, Fox noted.
He said Wednesday he was pleased a same-sex marriage bill was passed and signed into law in Minnesota and is optimistic about the repeal of Proposition 8, a 2008 referendum in California that only recognizes marriages as those between a man and a woman.
A ruling on the law's legality is expected from the U.S. Supreme Court in June.
Kluwe signed a one-year contract at the league minimum salary, Fox said. As a Viking in 2012 he averaged 45.0 yards on 72 punts.