US senator Susan Collins has said she will vote to confirm Ketanji Brown Jackson, giving Democrats at least one Republican vote and all but assuring that Ms Jackson will become the first black woman on the Supreme Court.

Ms Collins said in a statement that she met Ms Jackson a second time after four days of hearings last week and decided “she possesses the experience, qualifications and integrity to serve as an associate justice on the Supreme Court”.

“I will, therefore, vote to confirm her to this position,” the Maine senator said.

Her support gives Democrats at least a one-vote cushion in the 50-50 Senate and is likely to save them from having to use vice president Kamala Harris’s tie-breaking vote to confirm President Joe Biden’s pick.

It is expected that all 50 Democrats will support Ms Jackson, though one notable moderate, Arizona senator Kyrsten Sinema, has not yet said how she will vote.

Senate Democratic leaders are pushing toward a Judiciary Committee vote on the nomination on Monday and a final Senate vote to confirm Ms Jackson late next week.

White House chief of staff Ron Klain tweeted that he was “grateful” to Ms Collins for “giving fair, thoughtful consideration” to Ms Jackson and to other lower court nominees she has supported.

Ms Jackson, who would replace retiring Justice Stephen Breyer, would be the third black justice after Thurgood Marshall and Clarence Thomas, and the sixth woman.

She would also be the first former public defender on the court.

Ms Collins was the most likely Republican to support Ms Jackson, and has a history of voting for Supreme Court nominees picked by presidents of both parties.

The only nominee she has voted against since her election in the mid-1990s is Amy Coney Barrett in 2020.

Ms Collins said she does not expect she will always agree with Ms Jackson’s decisions, but added: “That alone, however, is not disqualifying. Indeed, that statement applies to all six justices, nominated by both Republican and Democratic presidents, whom I have voted to confirm.”

She added that she believes the process is “broken” as it has become increasingly divided along party lines. When she first went to the Senate, Supreme Court confirmations were much more bipartisan.

“In my view, the role the constitution clearly assigns to the Senate is to examine the experience, qualifications and integrity of the nominee,” she said. “It is not to assess whether a nominee reflects the ideology of an individual senator or would rule exactly as an individual senator would want.”

In Ms Jackson’s hearings, several Republican senators interrogated her on sentencing decisions in her nine years as a federal judge and in child pornography cases in particular.

The senators, several of whom are eyeing a run for president, asked the same questions repeatedly in an effort to paint her as too lenient on sex criminals.

She told the committee that “nothing could be further from the truth” and explained her sentencing decisions in detail. She said some of the cases had given her nightmares and were “among the worst that I have seen”.

It is unclear if any other Republican senators will vote for Ms Jackson.

Senate Republican leader Mitch McConnell said last week said he will not support her, citing concerns about her sentencing record and support from liberal advocacy groups.