Massachusetts state Rep. Dan Winslow (R) has decided to run for the Senate in Massachusetts, he said Thursday. He's the first Republican to officially throw his hat in the ring.

"I’m going to be 100 percent running for the U.S. Senate,” Winslow, a former aide to then-Massachusetts Gov. Mitt Romney, told the Boston Globe. “This is a heavy lift. I’m going to give this race everything I’ve got.”

Winslow's decision is not a surprise. He announced earlier this week that he was forming an exploratory committee.

The GOP faces a steep uphill climb in the race. A handful of well-known Republicans, including former senator Scott Brown, have passed on the race. Winslow may not be the only Republican who will run. Another name to keep an eye on is businessman and former Navy SEAL Gabriel Gomez.

On the Democratic side, longtime Rep. Ed Markey (D) is the frontrunner against Rep. Stephen Lynch (D), a more conservative Democrat.

The primary election is April 30, while the general election will be June 25.