The first all-female card in British boxing was headlined by a blockbuster fight which Shields won by unanimous decision as she claimed the WBA, IBF, WBO, WBC and Ring Magazine titles.
Marshall and Shields have been rivals for 10 years since they first clashed at the 2012 world championships in China.
"Claressa is a brilliant fighter - not as fast as I thought!" Britain's Marshall told Sky Sports.
"She has definitely earned the title of the Greatest Woman of All Time."
Shields said it was a special night for women's boxing and described it as the "fight of the year".
"Women's boxing has been around for so many years and there are so many greats who came before us, but here we are in front of 20,000 fans in London at the O2 Arena," a tearful Shields said after extending her undefeated professional record to 13-0.
"That was definitely the hardest fight of my career.
"She's a hard puncher. But I'm the better fighter 10 years later."
