The 23-year-old Brazilian has signed a four-year deal, having flown to England on Sunday after he earlier scored in Rennes" 2-2 draw with Reims.
He is Leeds" 13th summer arrival; with previous transfers including record signing Rodrigo and defenders Robin Koch and Diego Llorente.
Raphinha had a tally of eight goals and made seven assists in 36 appearances for Rennes.
He will wear the number 18 shirt at Leeds and could make his debut after the international break, when his side host Wolves at Elland Road.
He joined Rennes in September 2019 having previously had spells in the Portuguese league with Vitoria Guimaraes and Sporting Lisbon.
The signing ends Leeds" search for another wide attacking player in this window.
Boss Marcelo Bielsa had been hoping to bring in Manchester United"s Daniel James, who came very close to joining them from Swansea on deadline day in January 2019.
But they refused to release the Welshman amid uncertainty over their own pursuit of Jadon Sancho.
His signing takes Leeds" spending to about the £90m mark on first-team signings since they were promoted to the Premier League as Championship winners last season.
As well as the three aforementioned players, they converted the loan singings of Illan Meslier and Helder Costa into permanent deals, while also bringing in a number of players to initially play in their under-23 side.
However, a deal for French midfielder Michael Cuisance failed last week.
The transfer window closed at 23:00 BST on Monday – although a domestic window for moves between Premier League and Football League clubs will run until 16 October.
