He announced his decision to quit in a statement issued by the Football Association on Tuesday morning, following the team's defeat to Spain in the Euro 2024 final on Sunday night.
"As a proud Englishman, it has been the honour of my life to play for England and to manage England. It has meant everything to me, and I have given it my all," said Southgate.
"But it's time for change, and for a new chapter. Sunday's final in Berlin against Spain was my final game as England manager."
Southgate took charge in 2016, following the team's ignominious exit to Iceland in that summer's Euros and the short-lived reign of Sam Allardyce.
"I have had the privilege of leading a large group of players in 102 games. Every one of them has been proud to wear the Three Lions on their shirts, and they have been a credit to their country in so many ways.
"The squad we took to Germany is full of exciting young talent and they can win the trophy we all dream of. I am so proud of them, and I hope we get behind the players and the team at St George's Park and The FA who strive every day to improve English football, and understand the power football has to drive positive change.
"Thank you, England - for everything."
England lost 2-1 to Spain in Sunday's showpiece and Southgate said after the game he would discuss his future in charge of the national team.
England have only won the World Cup in 1966 but Southgate transformed the side which became a force to reckon with in tournaments after beginning his tenure in 2016.
They also reached the quarter-finals at the 2022 World Cup, a year after losing to Italy on penalties in the Euros final.
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