Democrat John Edwards endorsed former rival Barack Obama on Wednesday, a move designed to help solidify support for the party's likely presidential nominee even as Hillary Rodham Clinton refuses to give up her long-shot candidacy.

Edwards made a surprise appearance with Obama in Grand Rapids, Mich., as the Illinois senator campaigns in a critical general election battleground state.

The endorsement came a day after Clinton defeated Obama by more than 2-to-1 in the West Virginia primary. The loss highlighted...