BOSTON — Although his time in the U.S. Senate will be brief — less than five full months — William “Mo” Cowan could find himself in the thick of major policy debates from the federal budget to immigration reform and gun control.

Democratic Gov. Deval Patrick on Wednesday appointed Cowan, his former chief of staff, to serve as the interim U.S. senator for Massachusetts until a special election is held June 25 to fill the seat left vacant by John Kerry’s confirmation as the nation’s next secretary of state.

Cowan, 43, will be the state’s second African-American senator. Edward Brooke, a Republican, served two terms from 1967-1979.

In the wake of the “fiscal cliff” agreement Jan. 1 and looming automatic spending cuts, known as sequester, expected to take effect in March, Cowan said he backed a balanced approach to the nation’s fiscal woes that include some spending cuts and new revenues.

“I don’t think anyone believes it’s in the best interests to do straight across-the-board cuts,” he said.

“If a sequester happens, it’s going to have significant impact on Massachusetts,” he added. Some of the cuts could target grants to the state’s highly regarded universities and research facilities.

Cowan, 43, stepped down last month as chief of staff, a post he assumed in 2010 after previously serving as Patrick’s chief legal counsel.

Patrick lauded Cowan for helping manage the state through the recession and said he had earned the respect of people throughout government.

“In every step, he has brought preparation, perspective, wisdom, sound judgment and clarity of purpose,” Patrick said while introducing Cowan at a Statehouse news conference.

Patrick and Lt. Governor Timothy Murray added that the affable Cowan — who eschewed his trademark bowtie in favor of a traditional suit and necktie for Wednesday’s announcement — also brings a certain amount of “cool” to the job.

Cowan grew up in North Carolina and graduated from Duke University and Northeastern University’s law school. He was a partner in the prominent Boston law firm of Mintz Levin before going to work for Patrick, the state’s first black governor.

Cowan noted Wednesday that his mother, who is recuperating in North Carolina after knee-replacement surgery, was a child of the segregated South who raised him and his sisters alone after his father died when Cowan was a teen.

White House spokesman Jay Carney said Wednesday that he believes President Obama will be encouraged by the appointment of Cowan, along with a record number of female senators, “because he believes that diversity adds to the quality of debate.”

In the days leading up to the selection, Patrick said that he would consider diversity in his choice of interim senator. He had also insisted that the interim appointment be someone with no interest in holding the job permanently, and Cowan went further on Wednesday by saying he had no intention of running for any elected office in the future.

“This is going to be a very short political career,” he joked.

Former Democratic U.S. Rep. Barney Frank, who recently retired after more than three decades in the House, had been the only person to publicly express interest in the interim post and Patrick had acknowledged that Frank was among those he had considered.

Wednesday was the second time that Patrick has selected an interim U.S. senator. In 2009, following the death of Sen. Edward Kennedy, Patrick named Paul Kirk, a Democratic party operative and Kennedy family friend, to serve until a January 2010 special election that was won by Republican Scott Brown.

Under Massachusetts law prior to 2004, governors appointed a senator to serve until the next regularly scheduled state election. The Democratic-controlled Legislature changed the law after Kerry became the 2004 Democratic presidential nominee to block then-Gov. Mitt Romney from appointing a Republican in case Kerry won the election.

Brown, who lost his re-election bid to Democratic Sen. Elizabeth Warren in November, is “leaning strongly” toward running in the upcoming special election, according to Republican officials who spoke to the Associated Press Tuesday on condition of anonymity because they were not authorized to share internal discussions.

Two Democratic congressmen, Edward Markey, of Malden, and Stephen Lynch, of Boston, are expected to formally enter the race in the coming days. Kerry is among several leading Democrats who are backing Markey.

Kerry’s resignation from the Senate takes effect Friday, making Warren the state’s senior senator despite having been in the Senate for only a few short weeks herself.