The Cameroon midfielder completed his long-awaited transfer to Old Trafford after a prolonged saga.
The 22-year-old becomes United’s third midfield signing of the summer as they strengthen their squad.
"I came here at 19 with little English and no idea what this club would become to me,” Baleba wrote on Instagram.
"Brighton only asked me to be myself. The staff who make the club run so well. The teammates who took the time to understand me, on the pitch and off it. The nights at the Amex when I heard my name from that stand always made me feel at home.
"To all of the fans, staff and my team-mates. You looked after me and for that I will hold you all close to my heart. Wherever I play, this club is in how I play. Good luck Seagulls."
