Martin Looney, an unassuming but powerful lawmaker and influential New Haven politico, is in line for the top leadership role in the Connecticut State Senate.

Looney, currently the body’s majority leader, is expected to succeed Senate President Pro Tempore Donald Williams Jr. Williams announced Wednesday he will not seek reelection this fall, thus leaving his leadership position vacant and paving the way for Looney’s promotion.

With widespread party backing, Looney need only ensure Democrats maintain their majority in the Senate to take the chamber’s helm later this year. Expressing cautious optimism his party will remain dominant — it was 1994 when Republicans last took the majority — Looney said he is looking forward to leading the legislative body in which he has served since 1993.

“I’ve had an interest in this position for a while,” said Looney, who represents the eastern half of New Haven and part of Hamden. “It’s the most significant leadership position in the Senate.”

He added that he is gratified by the “many commitments of support” he has received from Democratic caucus members.

Williams, who has served alongside Looney in the State Senate for more than two decades, said he considers Looney a friend and supports his run for party leadership. Even more than his legislative accomplishments, Williams said, Looney’s “thoughtfulness” and deep pride in representing his constituents qualify him for the role of president pro tem.

The president pro tem is tasked with selecting committee chairmanships, making all committee assignments and ultimately shaping the caucus’ top priorities for each legislative session. By deciding when key bills are taken up, Williams said, the president pro tem exerts significant influence over the Senate’s agenda.

Williams said his deep affection for the legislative process made the decision to step down difficult. He is the longest-serving president pro tem in the state’s history, having led the caucus for 10 years.

“This is a good time to challenge myself and move in a different direction,” Williams said. “I’m still enthusiastic and passionate about my work. I certainly wouldn’t want to stay to the point that I did not feel that way.”

As for what he will try his hand at next, Williams said he has not yet decided: in addition to being an attorney, he also worked as a reporter before winning election to the State Senate.

Looney’s colleagues, friends and longtime political allies praised the state senator as an effective legislator and a compassionate voice for his constituents — with an unmatched knowledge of the state capitol and an unmistakably wry sense of humor.

Connecticut State Rep. Roland Lemar, a former New Haven alder, said Looney’s ascent is a coup for New Haven.

“Selfishly as a New Haven resident, I think it’s outstanding that Senator Looney will be moving into this spot,” Lemar said. “He’s been focused on urban issues for a long time. He understands fiscal policy, education, unemployment, job training — things that really impact urban communities.”

Lemar pointed to Looney’s leadership on the passage of the state’s first Earned Income Tax Credit in 2011 as evidence of the senator’s ability to muster votes despite partisan divisions.

With power in Hartford has come increasing sway in New Haven politics. Looney was part of a group of people who urged Mayor Toni Harp to run for the city’s highest office last year, a move he was rumored to be considering, especially after his law partner, probate judge Jack Keyes, declined to enter the race.

“[Looney] is very unassuming and very gentle, but he’s also very passionate in his beliefs,” said Keyes, a former city clerk who has been in practice with Looney since 1985. Keyes said Looney’s progressive values are long-lasting: He has favored public financing and gay marriage and opposed capital punishment for three decades.

Looney’s close ties to Harp stand in stark contrast to his relationship with former New Haven Mayor John DeStefano Jr., whom he ran unsuccessfully to unseat in 2001.

Keyes attributed Looney’s growing influence in New Haven to his role as majority leader, which he took on in 2004.

“The breakthrough was getting elected majority leader,” Keyes said. “That kind of changed the equation. A mayor needs a majority leader.”

Jason Bartlett, Looney’s campaign manager in 2001, said the state senator’s humble nature belies a “steely determination.” 12 years after managing Looney’s unsuccessful mayoral bid, Bartlett returned to New Haven to run Harp’s successful 2013 campaign. He now serves as the city’s director of youth services.

“I’m excited for the city of New Haven to have him in the number one spot,” Bartlett said. “It’s going to pay dividends.”

Looney was born in New Haven in 1948.