The Scotland striker has joined Fulham on a four-year contract, with the option of a further 12 months, for an undisclosed fee believed to be around £11m.
McCormack, who was top scorer in the Championship last season with 29 goals, is Felix Magath’s fifth summer signing following the arrivals of Tim Hoogland, Adam Taggart, Kay Voser and Shaun Hutchinson.
Leeds owner Massimo Cellino was adamant he did not want to lose McCormack but finally agreed to the sale in the early hours of Tuesday morning.
McCormack's only comment in response came on his official Instagram account.
He wrote: "New start. Thanks for the good wishes. Devastated to leave Leeds under a cloud after 4 thoroughly enjoyable years. Will always be a fan."
The 27-year-old started out with Rangers, before spells at Motherwell and Cardiff City prior to his switch to Leeds in 2010.
Capped 11 times by Scotland, the Glasgow-born striker has scored twice for his country.
In a statement on their website, his new club said: "Fulham Football Club is delighted to announce the signing of Ross McCormack from Leeds United for an undisclosed fee.
"The Scotland international, last season's top scorer in the Championship, has signed a four-year deal with the Whites, with the option of a further 12 months, potentially keeping him at the club until the summer of 2019."