The 65-year-old has been out of the game since his surprise sacking by Tottenham on June 14 despite leading them to a fourth-placed finish in the Barclays Premier League last season.
But Redknapp has now agreed to return to Bournemouth - where he began his career in management in 1983 - to offer advice and expertise to the npower League One club.
Redknapp enjoyed a successful time at Bournemouth, helping them escape relegation from the Football League in his first season in charge before producing a shock FA Cup win over holders Manchester United.
The Cherries were crowned Third Division champions in the 1986/87 season but were relegated several years later and Redknapp quit the club in the summer of 1992.
Redknapp will travel with the squad to Saturday's league clash with Yeovil at Huish Park.
Chairman Eddie Mitchell told the club's official website, afcb.co.uk: "I met Harry for a chat this morning [Friday] and he offered to come in on a voluntary basis.
"He still has a passion for the club and for football and he's got too much to offer for us to let him slip through our fingers.
"It's been in my mind for quite some time to get him involved, and the timing seems to be perfect for us to tap into his knowledge."
Manager Paul Groves and assistant Shaun Brooks were members of Redknapp's backroom team during his second spell as Portsmouth manager, which saw them win the FA Cup in 2008.
Mitchell added: "Paul and Shaun will still have the final say on all football matters, there's no doubt about that.
"They're very astute people and they're not above listening to anyone and I'm sure they can learn from him."
After leaving Bournemouth, Redknapp joined West Ham as an assistant to manager Billy Bonds and took over first-team affairs in 1994, tasting further success by leading the Hammers into Europe.
Redknapp went on to manage Portsmouth, steering them to the Division One title in 2002-03, before resigning in November 2004 and taking over at their south-coast rivals several weeks later.
But he failed to keep Southampton in the top flight and quit after less than seven months in charge - returning to Portsmouth.
In his second spell at Fratton Park, Redknapp guided the club to seventh place in the top flight - their highest league finish since the 1950s - as well as FA Cup success and a place in Europe for the first time in their history.
He took over as Tottenham boss in October 2008, leading them to a League Cup final in his first season and was named the Premier League manager of the year - the first time for an Englishman - as the club finished fourth in 2010-11.
Spurs again came fourth again last season but missed out on the Champions League courtesy of Chelsea winning the competition and Redknapp would later be sacked.