And then there were six.

Connecticut State Senator Toni Harp ARC ’78 announced Monday that she will run for mayor of New Haven, making her the sixth candidate vying to succeed Mayor John DeStefano Jr. Harp, who previously said she was not going to run, is now planning to file official campaign paperwork at the end of the week. If she wins, she will be the first female mayor in New Haven history.

“I’ve had a lot of experience and I’m used to working with other people … I respect the legislative branch and I understand its importance in helping frame policy that affects every level of government, and that’s what I would do as mayor,” Harp said. “I’ve been in the Senate for the past 20 years and have worked really hard to ensure that we have the resources that we need in our city to make it as successful as possible.”

Harp added that she has a “strong sense of policy” and that she was part of the group that instituted community policing in New Haven, which has seen a resurgence in recent years, when she served on the Board of Aldermen before going to work in Hartford in 1993.

At 65 years old, Harp is an 11-term incumbent state senator representing portions of New Haven and West Haven. She co-chairs the Appropriations Committee, in which she has played a major role in shaping state budget agreements, as well as the Mental Health Working Group under the state’s Bipartisan Task Force on Gun Violence Prevention and Children’s Safety. With Harp at the helm, the Appropriations Committee voted Friday to approve final recommendations for balancing the $43.3 billion state budget.

Harp said that after finishing her committee work, she has had time to reconsider her decision about entering the mayoral race, a move that many in the city expected her to make immediately following DeStefano’s January announcement that he would not seek re-election after 20 years in office.

Fellow Connecticut State Senator and Senate Majority Leader Martin Looney said he confidently endorses Harp and plans on “actively supporting her.” He particularly praised Harp’s leadership in devising state budgets as Appropriations Committee co-chair and lauded her work on municipal aid programs and “raise the age” legislation, which seeks to foster juvenile justice.

“She will be a superb mayor and a unifying force in the city,” he said.

Looney previously said he would support the potential candidacy of probate judge Jack Keyes, who owns a law practice with Looney. But with Keyes out and Harp in, Looney has thrown his full weight behind his colleague in the senate.

When she files to run, Harp will enter a dense field of candidates. The five candidates who have already filed are former New Haven Economic Development Administrator Henry Fernandez LAW ’94, Connecticut Technology Council CEO and former president of the Greater New Haven Chamber of Commerce Matthew Nemerson, Connecticut State Rep. Gary Holder-Winfield, Ward 10 Alderman Justin Elicker FES ’10 SOM ’10 and plumber Sundiata Keitazulu. A likely seventh candidate is Hillhouse High School Principal Kermit Carolina, who remains in the “exploratory phase” of his campaign.

Nemerson, who said he has known Harp through her work as an alderman and then as a state senator, said he believes Harp can best serve New Haven in her current position.

“My position is that [Harp] is a very, very valuable asset to the next mayor if she stays in her seat. Her seniority is impossible to replace, and she has connections to the Appropriations Committee and she will be somebody who can use her influence to push what has become a very difficult state budget,” Nemerson said. “My position is she should stay where she is.”

Along with Nemerson, other candidates have said that Harp’s entry into the race will not change their approaches to the campaign. Elicker said he has learned that “politics is unpredictable” and that when he declared his candidacy this past December, he “would never have predicted that the field looks like it does now.”

Prior to Monday’s announcement that she will run, Harp had said that she would be supporting Holder-Winfield in his bid for the mayor’s office. Holder-Winfield said Harp’s entry is bound to change the race.

“Senator Harp is a well-known commodity. She has years of experience,” he said. “It’s going to have a change, but I’m not quite sure exactly what that change is.”

Keitazulu called Harp’s entry a “big change.”

“I’m going to have to campaign a little harder because I know she’s really recognizable,” Keitazulu said. “My ideas are about jobs and creating jobs. I think my question with Harp entering the race is, why hasn’t she done more to create jobs in the area?”

At a Fernandez campaign kickoff event Monday, Fernandez’s campaign manager Jim Doumas said the campaign remains “very confident” despite Harp’s entry.

Remarking on an issue that has already divided the current candidates, Harp said she will not use the Democracy Fund, New Haven’s public campaign finance system that limits individual contributions in return for matching funds and a block grant. Along with Fernandez and Nemerson, Harp will rely exclusively on private fundraising, and said that coming into the race so late prevents her from using the Democracy Fund effectively. Fernandez has explained his decision to opt out similarly.

Looney dismissed the question of campaign finance as a “relatively minor one,” explaining that Harp’s leadership capacities and campaign platform should matter more.

Harp has said that she is still working out her campaign team and platform and that she will announce details of both in the coming week and a half.