Quan, who had formed an exploratory committee for the 22nd Congressional District in April, said he wanted to avoid a "costly, divisive and lengthy" Democratic primary.
He said he conducted polling that showed DeLay has lost support among constituents and that he and Lampson had nearly equal support.
Quan must leave the council in six months because of city term limits.
Quan, who is of Chinese ancestry, made the announcement at Kim Son restaurant in Stafford, and said he plans to help bring out the Asian vote for Lampson. Asians make up about 10 percent of the district.
Lampson, who served four terms in the U.S. House from Beaumont before losing his seat following redistricting orchestrated by DeLay, attended the news conference and said he was pleased to have Quan's endorsement.