Platt, 44, was a team-mate of City manager Roberto Mancini at Sampdoria.
"David brings a wealth of experience to his role as coach here at City, and he will enhance what is already an excellent team of staff at the club," Mancini told the club's official website.
"We had a great relationship as team-mates many years ago and I know he will make an important contribution to the club.
"Having David here at the start of pre-season training was an important factor, and I am very pleased that the coaching team will be in place as we prepare for the start of an exciting campaign."
Platt, who was capped 62 times by England and also enjoyed spells as a player with Aston Villa, Juventus and Arsenal, joins City in time for the start of pre-season training next Monday.
He will work alongside assistant manager Brian Kidd and coach Fausto Salsano at Eastlands.
After retiring Platt had spells as manager of Nottingham Forest and England Under-21s.
He left his post as Under-21 boss in 2004 and has since worked in the media.
Source: PA
Source: PA