President Obama has chosen Loretta Lynch, the U.S. attorney in Brooklyn, N.Y., as his nominee to replace outgoing Attorney General Eric Holder -- ending widespread speculation over who might fill Holder's shoes and teeing up a nomination debate potentially during the lame-duck session.

Though several Republicans had wanted to wait to consider any successor until the new Congress is seated, the president plans to announce his pick on Saturday.

"Ms. Lynch is a strong, independent prosecutor who has twice led one of the most important U.S. Attorney's offices in the country," White House Press Secretary Josh Earnest said in a statement. "She will succeed Eric Holder, whose tenure has been marked by historic gains in the areas of criminal justice reform and civil rights enforcement."

Lynch, 55, is a Harvard Law School graduate and popular prosecutor who is currently serving her second stint as U.S. attorney for Eastern New York, which covers Brooklyn, Queens, Staten Island and Long Island.

She was appointed by Obama in 2010. If confirmed to fill Holder's post, she would be the first black female attorney general.

It was unclear how the nomination will be greeted by Republicans on Capitol Hill, who were often at odds with Holder over the course of his tenure. The party won a majority in the Senate on Tuesday, but will not take control until January.

It was also unclear if the Senate might wait on a vote until then.

Senate Minority Leader Mitch McConnell, R-Ky., who presumably will become the majority leader in the next session, issued a statement Friday night urging the Senate to wait until January to vote on the nomination.

"Ms. Lynch will receive fair consideration by the Senate," he said. "And her nomination should be considered in the new Congress through regular order."

Annmarie McAvoy, an attorney and former federal prosecutor who worked directly under Lynch during her first tenure as U.S. Attorney from 1999-2001, said, “She’s got a good reputation …she’s done some great work in her office. She’s not one to put her head in the sand. She’s hasn’t been afraid to go after corruption, things like that, against Republicans and Democrats.”

She described Lynch as well liked, respected and not likely to cause a stir politically. “I have not heard anything controversial about her – at all,” McAvoy told Foxnews.com.

“When you meet her she is very sweet and she is very personable, she is very bright. She handles herself beautifully, but she doesn’t shy away from controversy.”

Lynch grew up in Durham, North Carolina, the middle of three children. Her mother was a school librarian, her father a Baptist minister.

After Harvard, Lynch served as a federal prosecutor in New York’s Eastern District, receiving several key promotions over eight years until President Clinton nominated her as U.S. Attorney in 1998. After leaving that office in 2001, Lynch went into private practice specializing in commercial litigation, white collar criminal defense and corporate compliance issues before Obama appointed her in 2010 to return to her current post.

“President Barack Obama has chosen a great New Yorker as the country’s highest-ranking law enforcement official,” New York Mayor Bill de Blasio tweeted Friday after news of the nomination.

In her time as U.S. Attorney, Lynch has made a name for herself in a number of high-profile convictions, including a thwarted Al Qaeda-sanctioned plot to attack the New York subway system, and pursuing the head of a Mexican drug cartel for 12 murders. She also heads the government’s prosecution of Rep. Michael Grimm, R-N.Y., who has been charged with tax evasion but won re-election Tuesday night.

There have been no indications thus far if Lynch’s nomination will be as dramatic as other Obama picks.

Sen. Charles Grassley, R-Iowa, who is currently the ranking member of the Senate Judiciary Committee -- which must approve Obama’s nominee -- appeared welcoming in his comments Friday night.

“Being selected to serve as our nation’s top law enforcement officer is both a tremendous honor and responsibility. As we move forward with the confirmation process, I have every confidence that Ms. Lynch will receive a very fair, but thorough, vetting by the Judiciary Committee,” he said in a statement.“I look forward to learning more about her, how she will interact with Congress, and how she proposes to lead the department.”

Reports throughout the week suggested that Lynch was not an Obama insider so she doesn’t bring the baggage carried by other potential administration nominees.

“Unlike Eric Holder, who was very close to the president – in a way, too close – she doesn’t really have any relationship with President Obama,” said Fox News contributor Kirsten Powers. “I think that bodes well for her.”

Lynch is reportedly close to Holder, however, having served on his Attorney General’s Advisory Committee of U.S. Attorneys (AGAC), a 20-member body that provides counsel to Holder on policy.

Sen. Ted Cruz, R-Texas, who sits on the Judiciary Committee, has already indicated that he is unhappy Obama is making the nomination now, instead of during the new session, when Republicans will have the majority in both chambers. “Democrat senators who just lost their seats shouldn't confirm (a) new Attorney General,” he tweeted on Friday. “(They) should be vetted by (the) new Congress.”

The Associated Press contributed to this report.