Sessions, who resigned Wednesday at Trump's request, frequently drew the president's ire for recusing himself from the Russian Federation investigation. He said he had quit the role at the president's request.
Trump has long railed against Sessions, a former senator from Alabama who was an early and longtime supporter of his presidential campaign.
Mr Sessions was widely expected to step down in the wake of the USA midterm elections, which saw the Republican party retain their majority in the Senate, but lose control of the House of Representatives.
In a September, 2018 profile of Whitaker in The New York Times, Whitaker was described as a "Trump loyalist" that is known by some White House source to be Trump's "eyes and ears" in the Attorney General's office.
Trump and Whitaker personally discussed the prospect of his replacing Sessions just last month, according to The Washington Post.
Senator Lindsey Graham, a Republican representing SC, vowed to help President Trump find a worthy successor for Sessions.
"We thank Attorney General Jeff Sessions for his service, and wish him well!"
Last year Whitaker, who was a legal analyst for CNN as well as former USA attorney, wrote that he felt the Mueller investigation had gone too far in looking into Trump Organization financial records that were not related to the 2016 election.
Trump did not answer a direct question about Sessions during his news conference Wednesday, saying that on the whole he is "extremely" satisfied with his Cabinet. He also said that Whitaker should recuse himself given previous comments about defunding and putting limitations on the probe. Rejecting White House entreaties not to do so, Mr Sessions stepped aside from overseeing the Federal Bureau Investigation's probe of potential collusion between the Trump presidential campaign and Russian Federation. Though Sessions effectively used his AG position to further some highly criticized changes at the Justice Department (like instituting a zero-tolerance policy at the United States border and threatening to withhold federal funding from sanctuary cities) he did not always get along with the man in charge.
He also said Mr Sessions' replacement might reduce Mr Mueller's budget "so low that his investigation grinds nearly to a halt".
When asked if he would fire Mueller, as some critics have feared, Trump said, "I could have ended it any time I wanted, [but] I didn't".