WASHINGTON—With an unusually strong bipartisan vote Wednesday, the U.S. Senate approved a $15 billion bill lawmakers hope will spur job creation in the flat employment market.

The vote was 70-to-28, with 13 Republicans siding with the Democratic majority to approve the measure. This was a larger number of minority-party members to side with the Democrats on the legislation than the five who voted on a measure to advance the bill earlier this week.

Among...