Leicester complete treble swoop
Nigel Pearson's side booked their place in the English top-flight by winning the Championship and they have wasted no time strengthening the squad for the step up in class.
Albrighton was the most significant of the signings, with the 24-year-old agreeing to join on a free transfer from Aston Villa.
The winger will sign a four-year contract when his current deal at Villa expires on July 1, and he told Leicester's website: "I'm absolutely thrilled to be joining. Everything about Leicester City is moving forward at the moment and it's going to be a great football club to be a part of."
Former England centre-back Upson turned down the offer of a new contract at second tier Brighton in favour of joining Leicester, who are back in the Premier League after a 10-year absence.
The 35-year-old, who won 22 England caps and played at the 2010 World Cup, will sign a one-year deal on July 1 after his Brighton contract expires.
Leicester also confirmed young forward Barmby, son of former Tottenham and England star Nick Barmby, will arrive from Manchester United on a two-year deal in July.
The 19-year-old will go into the Foxes' development squad, Leicester announced on their website.
Barmby spent the second half of 2013-14 on loan with Hartlepool and has been capped at England Under-19 level.
The three new arrivals made it four signings by Leicester in the last 24 hours following the capture of Charlton goalkeeper Ben Hamer, who agreed a four-year deal.