The Blades paid a reported £150,000 to land the striker and has signed a contract at Bramall Lane for three years.
Sheffield United manager Neil Warnock told sufc.co.uk: "We thought that in the circumstances after a couple of our targets fell through, that he will be a good signing.
"He's had a stop-start time at Brighton but we`ll give him the chance to improve."
Kazim-Richards leaves the Withdean Stadium after only being their 14 months; during that time he started 26 games whilst making 18 substitute appearances and scoring six goals.
Although he won't be a first team regular as he is considered as 'one for the future' the 20 year old could make his debut in the home fixture against Blackburn Rovers on 9 September or in the Carling Cup Second Round against former side Bury.
Meanwhile; only Rob Scott was the former Blade to make a move; having left Oldham Athletic to join Macclesfield Town.