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...
1. Hammers make Lingard bid
West Ham have made an offer to Jesse Lingard’s representatives over signing the player on a free transfer. (Sky Sports) | Manchester United via Getty Imag
2. Fulham make Mbabu offer
Newly-promoted Fulham have made an offer for Wolfsburg right-back Kevin Mbabu. (Tutto Mercato Web) | Getty Images
3. Gunners target Martinez
Arsenal want Ajax centre back Lisandro Martinez but the Dutch club have raised his price tag above £35m amid interest from Manchester United. (Daily Mail) | Getty Images
4. Roma plot Veltman raid
Jose Mourinho’s Rome and La Liga outfit Sevilla are on the trail of Brighton defender Joel Veltman. (Sky Sports) | Getty Images