(CNN) - Democratic Sen. Joe Manchin announced Tuesday he won't run for governor of West Virginia in the 2020 election, ending speculation as to whether he would leave the Senate to return to his old job as chief executive.
"I have always said that 'public service is not self-service.' So, when considering whether to run for Governor, I couldn't focus just on which job I enjoyed the most, but on where I could be the most effective for the Mountain State," Manchin said in a statement released Tuesday. "Ultimately, I believe my role as U.S. Senator allows me to position our state for success for the rest of this century."
Manchin had won a tough reelection to his Senate seat in the 2018 midterms, beating his Republican opponent, West Virginia Attorney General Patrick Morrisey, by a little more than 3 percentage points.
Manchin has held the position of West Virginia governor before, first elected in 2004 and reelected in 2008 — which he called the "best job I have ever had."
He left the governor's office and won a special election for the US Senate in 2010, after the death of Sen. Robert Byrd left a vacancy. Manchin won a full Senate term in 2012.
"Those who know me know how much I loved being the Governor of West Virginia," Manchin said in his statement Tuesday. "I worked the daylights out of that job. I couldn't wait to wake up in the Governor's Mansion in the morning, and I didn't want to go to bed at night, because there was always more that I could do for our state."
Manchin has made no secret of his discontent with Washington and the US Senate, famously saying, "this place sucks."
When the governor's seat was open in 2016, Manchin toyed with leaving the Senate to run for governor, but ultimately decided against it. He later endorsed Jim Justice, a billionaire businessman who was at the time a Democrat. Justice had changed his party registration from Republican to Democrat to run for governor, but switched back to the GOP not even a year into his term. Justice is seeking a second term as governor.
West Virginia has been deeply red in recent elections with President Donald Trump winning the state by 42 percentage points in 2016.
During his time in the Senate, Manchin has built a reputation as the most conservative Democrat and has shown a willingness to work with Trump and Republicans.
Explaining his decision at a news conference later Tuesday in his home state, Manchin lamented the growing polarization between the major parties.
"There's nobody trying to find the middle. Everybody's going for the sides, if you will, for the extremes. Everybody thinks they're going to be far right or far left. It's not how you get things done," he said, adding, "You got to find that middle. And I think this country is going to come back to that. We have got to find the middle. And the middle is not that popular right now. There's not that many of us in it. So with all that said, I made the decision I made."
Manchin was invited by Trump to Trump Tower during the transition to discuss a potential Cabinet position as energy secretary and, since Trump has been in office, has made several visits to the White House.
He was the sole Democrat to vote to confirm Jeff Sessions as attorney general. He also broke with his party to vote to confirm conservative leaning judges Neil Gorsuch and Brett Kavanaugh to the US Supreme Court, two of Trump's lifetime picks to the high court.
But Manchin has also been critical of the President, opposing Trump's travel ban and Republican efforts to repeal Obamacare.
In his decision to stay in the Senate, Manchin cited his role as the top Democrat on the Senate Energy Committee, promising to "push the Senate to take up and pass energy technology bills" and work for an energy base that "recognizes the reality of climate change." He also pointed to his work on the Senate Armed Services and Veterans Affairs Committee, vowed to protect coal miners' pensions, and make sure that his home state "gets its fair share of federal resources."
Manchin also said he would work with Trump to "accomplish what best serves our state and our country and I will speak truth to power when I don't agree with the path the President has chosen to take."
This story has been updated.
CNN's Manu Raju, Eric Bradner, Ashley Killough and Lauren Fox contributed to this report.