Attorney General Maura Healey's entrance Thursday into the gubernatorial field not only shakes up that race, but sets the stage for a wide-open contest to succeed her as the state's top law enforcement officer.

Healey has served as attorney general since 2015 and defeated Republican Jay McMahon in 2018 to win reelection. Her announcement that she will seek the Democratic nomination for governor creates an opportunity for someone new to step into a prominent statewide office without first having to take on an incumbent.

Before Healey formalized her plans to run for governor, two Democrats and past contenders for statewide office, Quentin Palfrey and Shannon Liss-Riordan, had opened campaign accounts to run for attorney general.

Andrea Campbell, the former Boston city councilor who ran for mayor in 2021, also is seriously considering a bid to become the state's top law enforcement officer, according to sources close to her. Campbell served as deputy legal counsel in Gov. Deval Patrick's administration and, on the mayoral campaign trail, called for reforms to the policing and criminal justice systems.

A Palfrey spokesperson said a formal campaign announcement is forthcoming. The 2018 Democratic nominee for lieutenant governor, Palfrey congratulated Healey, with whom he has previously worked in the AG's office, on her decision. He has a virtual fundraiser planned for next Thursday, and a Tuesday campaign email about the event described the host committee as still in formation.

"As your Attorney General, I will serve as the people's lawyer, protecting consumers and tackling the really big problems we face in Massachusetts today: racial injustice, the climate crisis, and attacks on our democracy," Palfrey said in a statement. "I'm excited for the journey ahead and plan to build a grassroots campaign for AG that respects, empowers, and includes people from across the state."

Healey has often described herself as "the people's lawyer," and used that phrase Thursday in her first campaign video for governor.

Liss-Riordan, a labor lawyer who brought cases that forced policy changes at Starbucks, FedEx, Harvard University and American Airlines, mounted a primary challenge against U.S. Sen. Ed Markey in the 2020 election cycle, but dropped out of that race before the filing deadline.

She filed campaign-finance paperwork for an attorney general run on Dec. 6, 2021 and at the end of that month reported taking in just over $159,000. Palfrey reported raising more than $68,000 in December, and had a balance of $135,815 at year's end. Campbell, who raised $1.6 million toward her mayoral campaign, now has about $35,000 on hand.

Healey was first elected in 2014 out of another open-seat race, when her predecessor Attorney General Martha Coakley ran for governor.

Healey, a first-time candidate, bested Republican attorney John Miller after securing 62 percent of the primary vote to fellow Democrat Warren Tolman's 38 percent.

Another Democrat, then-Rep. Harold Naughton, had been in the race for a period but ended his campaign around the time the party started its caucuses.

Many state lawmakers have law degrees, including some who remain practicing attorneys. They also have existing campaign operations, as do county district attorneys who would be able to tout prosecutorial experience.

Middlesex District Attorney Marian Ryan's name has come up as a potential candidate. Ryan, a Belmont Democrat, has not yet said if she's running for reelection, and a campaign spokesperson said she has not ruled out an attorney general bid.

Open seats typically generate more interest than challenges against incumbents and can spark intense speculation. The field for attorney general historically has not been a particularly crowded one in Massachusetts.

State election records show the last time more than two AG candidates made it to the ballot for either party primary was in 1974, a contest for a seat that opened up when Attorney General Robert Quinn ran for governor.

That cycle, Quinn lost to Michael Dukakis in the Democratic primary. Republican attorney general hopeful Josiah Spaulding, after prevailing in a three-way primary, lost the general election to Francis Bellotti, who had defeated five other candidates vying for the Democratic nomination.

In a run that began with Quinn, a former House speaker, Democrats have held the attorney general's office since 1969. The last Republican AG was Elliot Richardson, who left to join the Nixon administration.

The 2022 ballot will feature several open seat races among the constitutional offices. In addition to governor, lieutenant governor and attorney general, a contest is underway for the position Auditor Suzanne Bump is vacating.

Treasurer Deborah Goldberg and Secretary of State William Galvin have not officially declared their electoral intentions. Democrat Tanisha Sullivan launched a campaign for secretary this week.