Newcastle accepted Barcelona’s offer of €80m (£69.3m) for Gordon, which is inclusive of add-ons, with the 25-year-old having signed a five-year deal with the La Liga champions.
Bayern Munich were initially favourites to sign Gordon, but refused to meet Newcastle's demands. Liverpool made a late attempt to set up a deal of their own last week, but Gordon had already expressed a preference for joining Barcelona.
He completed a medical on Thursday and was officially unveiled as a Barca player at a press conference last night after completing the final formalities of his transfer.
His departure makes him the second most expensive sale in Newcastle’s history, behind only Alexander Isak’s £125m switch to Liverpool last summer.
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Gordon was keen to complete his move to Barcelona before heading to the United States next week to prepare for England’s opening World Cup warm-up game against New Zealand a week today.
The 25-year-old finished the season as Newcastle’s leading goalscorer with 17 goals in all competitions, and the Magpies have already begun the process of lining up his replacement.
Newcastle’s recruitment team are understood to have been closely monitoring Lille forward Matias Fernandez-Pardo and Osasuna winger Victor Munoz, with both players regarded as potentially exciting options in the final third.
The Magpies have also been heavily linked with Real Betis winger Abde Ezzalzouli, a 24-year-old Morocco international who scored 15 goals and claimed 13 assists in 43 appearances last season.
There is also a determination to sign a new goalkeeper this summer, with Aaron Ramsdale set to return to Southampton ahead of the start of next season after Newcastle officials decided not to take up the option of a permanent move for the shot-stopper, who lost his place to Nick Pope in the second half of the current campaign.
Newcastle are known to have a strong interest in Reims goalkeeper Ewen Jaouen, an emerging 20-year-old who made 35 appearances in Ligue 2 last season.
The Magpies remain interested in James Trafford, who is weighing up his future at Manchester City after struggling for game time. Trafford rejected the opportunity to join Newcastle last summer in order to move to the Etihad Stadium.