The Warriors announced the signing late Tuesday night. Looney is expected to play in the team's first summer league game in Las Vegas on Friday.
There had been some concern about whether Looney would be able to play because of a previous hip injury. Warriors general manager Bob Myers said on draft night that the team would evaluate and monitor Looney's hip throughout the summer.
Golden State selected Looney with the 30th overall pick in last month's draft. He averaged 11.6 points and 9.2 rebounds per game in his lone season at UCLA, where he mostly played power forward.