Incumbent Sen. Susan Collins (R) and Troy Jackson (D) are running in the general election for the U.S. Senate in Maine on Nov. 3, 2026.

On July 10, 2026, Graham Platner (D), the winner of the 2026 Democratic primary for the U.S. Senate in Maine, withdrew from the general election following an allegation of sexual assault. As a result, the Maine Democratic Party held a nominating convention to select a new nominee. On July 25, 2026, Jackson won the nominating convention, marking the 28th time since 1918 that a new candidate was selected to replace a U.S. Senate nominee.

According to The New York Times' Reid J. Epstein and Jess Bidgood, "By replacing Mr. Platner with Mr. Jackson, Maine Democrats hope to make the race less about their candidate and more about painting Ms. Collins as a tool of the ultrawealthy and a rubber stamp for President Trump on the most pressing matters."

This U.S. Senate seat is the only one Republicans are defending in a state that Kamala Harris (D) won in the 2024 presidential election. Harris defeated President Donald Trump (R) in the state 52.4% to 45.5%. Politico's Jessica Piper and Aaron Phellish wrote that "[Collins'] bid will rely on a coalition that includes independents and Democrats, many of whom have backed her in the past because of her breaks from Trump and other GOP leaders."

Collins was first elected to the U.S. Senate in 1996. She previously served as commissioner of the Maine Department of Professional and Financial Regulation, New England regional director of the U.S. Small Business Administration, and deputy state treasurer of Massachusetts.

Collins is running on her experience in the U.S. Senate and as chair of the chamber's Appropriations Committee. According to her campaign website: "This committee decides how federal dollars are spent each year, from national defense and infrastructure to medical research, education, and public safety. Susan's position gives Maine an outsized voice at the table when critical decisions are made which allows her to deliver serious results for Maine."

Jackson served in the Maine Senate from 2008 to 2014 and from 2016 to 2024. During his tenure in the chamber, Jackson served as Democratic leader and Senate President. Jackson previously served in the Maine House of Representatives from 2002 to 2008 and worked as a logger.

Jackson is running on an economic populist message. He said, "Working people are getting crushed while billionaires and corporations buy power in Washington. I've spent my life fighting that same rigged system—from the logging woods to the Maine Senate. I'm running to carry forward Maine's working-class movement, defeat Susan Collins and give people a senator who will fight like hell for them—not the wealthy and well-connected."

Both Collins and Jackson are from Aroostook County, Maine. According to The Cook Political Report's Jessica Taylor, this election will be the first in which Collins will face a challenger from northern Maine: "It's a regional advantage that Collins, who is from the town of Caribou, has long held. All of Collins' previous opponents — including the 2020 nominee, House Speaker Sara Gideon — came from southern Maine and were not seen as authentically 'Maine' enough. Jackson won't have that problem."

As of July 28, 2026, The Cook Political Report, DDHQ/The Hill, and Sabato's Crystal Ball rated the general election as a Toss-up. Inside Elections rated it Tilt Republican.