The measure passed on a voice vote Monday, after clearing the Senate last Thursday.
Rep. Suzan DelBene said Monday it offers good news for the community of Darrington, which is reeling from last month's devastating mudslide that killed 33 people. The structure is popular with hikers, tourists and locals in the area.
The lookout was built in 1933, and the Forest Service used a helicopter and machinery to repair it in 2009. A Montana-based environmental group sued, saying such methods aren't allowed in federal wilderness areas.
A judge ordered it removed, but the state's congressional delegation has been trying to save it.
The bill now goes to the President, who indicated support for the lookout in February.