Rice played three senior internaitonal games for Ireland in 2018 having previously represented Ireland at underage level.
"I have equal respect and love for both England and Ireland and therefore the national team I choose to represent is not a clear-cut, simple selection", Rice said.
"This has been an extremely hard decision", Rice tweeted in a statement on Wednesday afternoon.
Rice had spent months deliberating on his decision with his family, girlfriend and friends as his stock has risen at West Ham, where he has made 27 appearances this season.
'Ultimately, it is a personal decision that I have made with my heart and my head, based on what I believe is best for my future'.
The 20-year-old added that he had reached this conclusion after discussions with those two worldwide managers, with the former Republic of Ireland manager Martin O'Neill and with his family and friends.
He also addressed the Irish fans in the statement, saying: "I fully accept that some Irish supporters will be disappointed by my decision, and that everyone has different opinions in regard to the rules around global representation".
"My pride at wearing the Irish shirt was 100 per cent genuine".
The switch of allegiances represents a devastating blow to the future of Irish football, with Rice widely regarded as one of the best players of his age in the world. Rice had been approached by England coach Gareth Southgate about playing for the nation of his birth.
He announced the news through a statement on his Twitter page on Wednesday.