RELATED: Montana GOP hopeful charged with misdemeanor assault against Guardian reporter
Gianforte defeated Democrat Rob Quist on Thursday to replace Ryan Zinke, who is now President Donald Trump's interior secretary.
Gianforte was elected despite being charged with misdemeanor assault on Wednesday after witnesses said he grabbed a reporter for the Guardian newspaper and slammed him to the ground.
The multimillionaire technology entrepreneur is an enthusiastic Trump backer, and his victory was seen as an endorsement of Trump.
Gianforte's campaign was boosted by rallies featuring Vice President Mike Pence and Donald Trump Jr. plus millions of dollars in ads by Republican groups.