The decision to leave his post comes after Mr Sessions endured more than a year of blistering and personal attacks from Mr Trump.
The move, which had been expected, was made on the recommendation of FBI disciplinary officials.
Many have already left their positions, but those who stayed on have been asked to leave "in order to ensure a uniform transition".
An early supporter of Donald Trump's presidential campaign, Attorney General Jeff Sessions has a very conservative background as a senator.
He faced opposition from Democrats over his civil rights record and immigration, while Republicans praised his 40 years of public service.