Moyles confirmed the news during his show at around 8am this morning (11th July), stating he will step down as host in September.
He stated: "We're off. I wanted to let you know. A couple more months of us, then it's someone else's turn. Thank you for listening."
The 38-year old then played the Take That classic Never Forget before continuing with the show.
Moyles took over the breakfast show from Sara Cox in 2004, raising its ratings from 9.73million to a high of 11.82million in 2010, with Radio 1 controller Ben Cooper stating: "I'd like to thank Chris. Quite simply, he's been the most successful breakfast show host in Radio 1 history.
"He's done it for more than eight and half years and he's been fantastic."
Grimshaw will now replace Moyles, with Fearne Cotton making the announcement live on air at 10.30am, adding that she was "very, very chuffed" for Nick, but would "miss Moyles a lot."
She claimed: "He's a dear friend of mine. He's just going to have a great time. He is free to do what he pleases."
Cooper said Grimshaw would be a "brilliant" fit for the Breakfast Show, adding: "Nick is a great broadcaster. He's got a passion for music, and has also got that great sense of humour as well."
Speaking of his new job, Grimmy said: "It’s been a dream of mine since the age of 11 and, to be honest, it hasn’t really sunk in yet. I love Chris and have always looked up to him as one of the best broadcasters ever.”
Watch MTV News on the hour every hour on MTV - Sky Channel 126 and Virgin Channel 134