Sessions' chief of staff, Matthew G. Whitaker, will be acting Attorney General. It's unclear at this time if the appointment will be made permanent.
President Trump has been openly upset with Sessions since the attorney general recused himself in March 2017 from an investigation over Trump's links to Russia.
Sessions cited his ties to the Trump campaign in his decision.
“How do you take a job and then recuse yourself?” President Trump said at the time, according to The New York Times. “If he would have recused himself before the job, I would have said, ‘Thanks, Jeff, but I can’t, you know, I’m not going to take you.’ It’s extremely unfair, and that’s a mild word, to the president.”
"At your request, I am submitting my resignation," Sessions' resignation letter said in a letter to President Trump.
"Since the day I was honored to be sworn in as Attorney General of the United States, I came to work at the Department of Justice every day determined to do my duty and serve my country. I have done so to the best of my ability, working to support the fundamental legal processes that are the foundation of justice," his letter continued.
"The team we assembled embraced your directive to be a law and order Department of Justice," Sessions' letter said. "We prosecuted the largest number of violent offenders and firearm defendants in our country's history. We took on transnational gangs that are bringing violence and death across our borders and protected national security. We did our part to restore immigration enforcement. We targeted the opioid epidemic by prosecuting doctors, pharmacists, and anyone else who contributes to this crisis with new law enforcement tools and determination. And we have seen results."
"After two years of rising violent crime and homicides prior to this administration, those trends have reversed—thanks to the hard work of our prosecutors and law enforcement around the country," Sessions added.
In his letter he thanked the men and women of law enforcement.
MoveOn and other activist groups have called for over 900 protests across the country to protest Sessions' firing.
The groups organizing the protest have been extremely critical of Sessions in the past.
Whitaker, Sessions' replacement, is a former U.S. Attorney for Iowa who previously wrote an opinion piece for CNN saying that the Russia investigation would be going too far if they dug into the president's personal finances.
"It does not take a lawyer or even a former federal prosecutor like myself to conclude that investigating Donald Trump's finances or his family's finances falls completely outside of the realm of his 2016 campaign and allegations that the campaign coordinated with the Russian government or anyone else," he wrote at the time.
His column has had him labeled a Trump loyalist by The New York Times and sparked concerns that his appointment is a move by the president to take control over the investigation.
The protesters will demand that Whitaker recuse himself from the investigation.