The 20-year-old arrives from Danish Superliga club FC Nordsjaelland, for whom he has played since January 2020.
Adingra, a product of Ghana’s Right To Dream Academy, scored 10 goals in 33 appearances last season.
Brighton technical director David Weir said: “We’re delighted to welcome Simon to the club.
“He’s an exciting young player who has had a terrific start to his career in Denmark.
“He’s a creative offensive player who can play on both sides and is very good in one-on-one situations.
“He’s a talented young player who we’ve had an eye on for a while, and we’re looking forward to helping him with his development.”
Last week Brighton agreed a £9.5m deal for 18-year-old Paraguay star Julio Enciso, who arrived on a four-year contract.
Check out the latest Premier League transfer speculation below...
Brighton technical director David Weir said: “We’re delighted to welcome Simon to the club.
5. Broja on Toon radar
Newcastle United have reportedly launched a formal approach for Chelsea striker Armando Broja, who is also a £30m transfer target for West Ham. (Northern Echo)
6. Leeds eye De Ketelaere
Leeds United are launching a £26m bid for Club Brugge forward Charles de Ketelaere. (Daily Mail)
7. Richarlison wants Spurs move
Richarlison is keen to quit Everton for Tottenham, and has told his friends that he wants to move to north London. (Football Insider)
8. Leeds consider Foster
Former Manchester United and Watford goalkeeper Ben Foster is ‘under consideration’ as a target for Leeds United. (Daily Mail)