Former New Hampshire Gov. Jeanne Shaheen has stepped down as the director of Harvard's Institute of Politics to run for U.S. Senate, the Kennedy School of Government announced Friday.

Shaheen, a Democrat, will vie in next year's election against John E. Sununu, the Republican senator who defeated Shaheen in 2002 when she ran for the seat.

Since 2005, Shaheen has led the Institute of Politics, the Kennedy School-based program known for bringing prominent leaders to Harvard and sponsoring programs for budding student politicians.

In an e-mail to the institute's student advisory committee on Friday, Shaheen said that she was sorry to leave Harvard so abruptly, but added that she had been working with Kennedy School officials to "exit in a way that best avoids compromising the Institute."

"[A]t the IOP we preach the importance of politics in making a difference in people's lives, and I believe I can make a difference in New Hampshire by entering the Senate race," Shaheen wrote.

Kennedy School Dean David T. Ellwood ’75 said that the school had been aware that Shaheen was considering a Senate run and would announce a replacement early next week.

“Jeanne has been an effective engaged, nonpartisan leader of the Institute of Politics, and we are truly sorry to see her go,” he said in a written statement.

Shaheen took the Harvard position after serving as the national co-chair of Democratic Sen. John F. Kerry's 2004 presidential campaign.

During Shaheen’s short tenure, the institute launched a women’s leadership program and expanded internship opportunities for undergraduates.

In New Hampshire, Shaheen will compete in a state that has trended increasingly Democratic in recent years. In 2004, New Hampshire voters chose Kerry over George W. Bush, and elected a Democrat, former Harvard Business School admissions director John Lynch, to serve as the state's governor.

In addition, both of New Hampshire's moderate Republican congressmen were defeated by Democratic challengers in 2006, and Democrats took control of the state government for the first time since 1874.

Shaheen's entrance into the race immediately turns New Hampshire into a marquee race, joining Colorado, Virginia, and Minnesota as top Democratic takeover attempts. According to a July poll conducted by the University of New Hampshire Survey Center, Shaheen would handily defeat Sununu by a 54 to 38 margin.

Democratic Party officials have pushed Shaheen to enter the race, and Sen. Edward M. Kennedy '54-'56 reportedly played a key role in persuading Shaheen to run.

Kennedy, a member of the institute’s senior advisory committee, praised Shaheen’s two years of service.

“I’m sure this was a very difficult decision for her, because she’s done such an excellent job at the Institute and has been an inspiration to so many outstanding young students to consider careers in politics and public service,” he said in a written statement.

—Staff writer Paras D. Bhayani can be reached at pbhayani@fas.harvard.edu.