Senate President Thomas V. Mike Miller Jr. announced Thursday he will end his unparalleled three-decade tenure leading the chamber, a reign so dominant that it shaped the course of Maryland policy for a generation.

A centrist Democrat and deeply skilled political strategist who could predict the passage or death of virtually any bill, Miller told The Washington Post that his battle with cancer had sapped his energy and he did not want “to be perceived as lingering on or trying to hold on to something past my time.”

Miller, 76, is the country’s longest-serving senate president. He has wielded power in the Maryland Senate since before some current senators were born.

He said he will cede the presidency but intends to serve the remaining three years on his term as a rank-and-file senator. “I don’t intend to go cut the cord completely,” he said in an phone interview from a hospital room earlier this week. The interview was embargoed until Miller announced his decision.

Senate Democrats, who hold 32 of the chamber’s 47 seats, voted in a closed-door caucus meeting Thursday to back Sen. Bill Ferguson (D-Baltimore City) as Miller’s successor.

Ferguson, 36, an attorney and former teacher who is a strong advocate of revamping and investing more in public education, had not yet entered kindergarten when Miller took control of the Senate.

Miller shared his decision to step down with his Democrat colleagues at the caucus meeting held in the Miller Senate Office Building, which was dedicated to him 19 years ago.

Since 1987, Miller, a devout Catholic, has been a larger-than-life figure in the Maryland General Assembly, known for his backslapping charm and cunning as a political tactician. Most major policy decisions in the state — from casino gambling and tax structure to same-sex marriage and abortion rights — became law either through Miller’s force or acquiescence.

“He often says, ‘I can’t predict the future, but I’m going to tell you what’s going to happen’,” said Robert R. Neall, a longtime friend and former senator. “Both are true. He really doesn’t predict the future, but he influences the future.”

Miller announced in January he was undergoing chemotherapy for Stage IV prostate cancer that had metastasized in his bones. He vowed to stay at the helm of the chamber as long as his health allowed.

This week, he spent four days at Johns Hopkins Hospital in Baltimore to be treated for complications of his cancer treatment. The day after he was released, he spoke at a memorial service for longtime Rep. Elijah E. Cummings at Morgan State University.

Miller said his cancer has not worsened, but his weakened immunity and a string of complications starting in July — which include a bout of shingles and a broken rib and vertebrae from a fall — persuaded him he could not keep up the grueling schedule of a Senate president.

“Physically, I’m fine. Mentally, I’m fine,” Miller said. “But it’s also time to move on. It’s inevitable, so there’s no better time than now.”

He said he still has enough energy to keep up with public events in his legislative district, but not those statewide.

“Anybody who follows me on Facebook knows that I keep up the regular daily schedule, going to events and responding constituent’s problems and needs. And I enjoy that. That’s an important part of my life,” Miller said.

His resignation creates a leadership transition as Democratic lawmakers prepare to battle with Republican Gov. Larry Hogan over school funding. Miller said he plans to remain central in that fight and intends to spend the next year persuading Hogan to invest more in public schools.

“It bothers me that [Maryland’s] education is not No. 1 in the United States of America,” Miller said.

Hogan and Miller sparred on policy during the governor’s five-year tenure, but they also treated each other with affection and as worthy adversaries. As a teenager, Miller had worked for the governor’s father, a former congressman and Prince George’s County executive. Miller at one point babysat a 5-year-old Hogan while his dad was on the campaign trail.

In a statement, Hogan praised Miller as “a strong, unifying leader for the legislature and the state. His steady presence and trademark humor will be deeply missed as President, but we are pleased to know that Mike will continue to represent Calvert County as he begins his 50th year in the Senate.”

Miller, a history buff, has proved time and again to be a nimble leader who could steer the Senate through shifting political currents.

“Mike could see things before they happened,” said Vicki Grueber, his chief of staff for a third of his tenure. “He can see how things are going to go and how it’s going to happen before it does. He was a student of history, and history repeats itself.”

As the Senate grew younger and more liberal over the years, Miller survived a coup attempt in 2000. He cultivated influence by studying the lives and districts of his members, and his grip on power remained ironclad.

In the earlier years, it was part through intimidation and salty temper. He once sent a menacing Christmas card to a lawmaker whose vote he disliked. Another time, he shoved a meddling lobbyist against a wall.

In later years, Miller’s force was a more nuanced mix of fundraising prowess and political acumen. Among other tactics, he was a prolific donation bundler for his members. He was willing to ensure each of the 46 other Senators — the Republican minority included — could either take home a policy win to their districts or would not be forced into an untenable vote.

He enjoyed unshakable loyalty from his colleagues, many of whom, as they watched his health degrade over the summer, believed he was in worse shape than he publicly revealed.

“He loves what he does,” said one veteran senator who requested anonymity to discuss sensitive matters. “Like in the old cowboys movies, he’d probably decide to die in the saddle if it was up to him.”

This winter, Miller announced he would not seek reelection in 2022, at the end of his current Senate term. Already, The College of Southern Maryland announced the creation of the Thomas V. Mike Miller, Jr. Center for Leadership to honor him.

Miller choked up five times during his 25-minute interview with The Post. He blamed a cancer treatment that starved his body of testosterone, joking that without it, he is a little more emotional than normal.

With the extra time he will get back by not doing building dedications and ribbon-cuttings around the state, “hopefully, I will concentrate on my health,” Miller said. “I’ll be like one of the other state senators, focusing on constituent service.”