Gianfranco Zola had overseen a torrid run of form in 2017 that leaves Birmingham three points off the drop zone with as many games to go and resigned on Monday following a 2-0 defeat to Burton Albion.
Redknapp, with his 34 years of managerial experience, has subsequently been chosen to rescue them from potential relegation, with Birmingham set to face Midlands rivals Aston Villa this weekend.
The club will then face promotion-chasing Huddersfield, and 18th-placed Bristol City as the club desperately attempts to avoid the Championship trapdoor.
The 70-year-old has been out of work since ending his short stint in charge of national team Jordan last year.
Redknapp has been involved in football since 1958, and has managed Bournemouth, West Ham, Southampton, Tottenham, QPR and Jordan, and has also taken in two stints at Portsmouth, where he won the FA Cup.
Redknapp is currently listed as a director at non-league Wimborne Town, and a football consultant at Australian club Central Coast Mariners. It remains to be seen if he will step down from those two roles in order to focus on survival at Birmingham.