The Prime Minister’s senior aide resigned in a tearful statement outside her north London home on Wednesday.
The decision came after footage of Ms Stratton emerged at a mock press conference answering questions about a Downing Street Christmas party.
Staff in Downing Street are believed to have held a Christmas party, despite repeated denials from Downing Street.
In a tear-filled press conference, Ms Stratton said: “My remarks seemed to make light of the rules, rules that people were doing everything to obey.
“That was never my intention. I will regret those remarks for the rest of my days and offer my profound apologies to all of you for them.
"I understand the anger and frustration that people feel.
“To all of you who lost loved ones, endured intolerable loneliness and struggled with your business – I am sorry and this afternoon I have offered my resignation to Prime Minister”.
Ms Stratton's switch from journalism to government spinner was a controversial one, with many of her colleagues in Westminster predicting it could all end badly.
Having graduated from Cambridge University, she began her media career as a producer for the BBC before moving into print journalism and working as a political correspondent at The Guardian.
Ms Stratton joined BBC Newsnight as political editor in 2011 before becoming national editor at ITV News in 2015 and also co-presented ITV’s Peston On Sunday.
In 2011, she married James Forsyth, the political editor of The Spectator, the conservative magazine which the Prime Minister used to edit.
Ms Stratton left journalism in April last year to become the director of strategic communications for Chancellor Rishi Sunak.
The Prime Minister was said to have been “impressed” with Ms Stratton’s abilities while working at the Treasury and convinced her to become the public face of Downing Street as Mr Johnson’s press secretary in televised press briefings.
In April, Ms Stratton was moved to become the spokeswoman for COP26 President Alok Sharma before she could front a single briefing. It was her ultimately doomed period training to become the No 10 press secretary, however, that prompted her resignation.