WASHINGTON—A GOP-led Senate committee backed U.S. intelligence agencies’ finding that Moscow tried to boost Donald Trump’s 2016 presidential campaign by hacking and spreading misinformation, a bipartisan conclusion that breaks with a House panel’s position and the president’s rejection of the notion that Russia wanted him to win.

The Senate Intelligence Committee’s conclusion, made public Wednesday after a closed-door hearing with former intelligence chiefs, is part of the panel’s continuing probe, begun 14 months ago, into...