Mr Miliband, who was succeeded by Jeremy Corbyn after leading the party to electoral defeat, was named as the new shadow business secretary on Monday.
Mr Milliband said he was "looking forward to serving in Keir Starmer's Shadow Cabinet as Shadow Business and Energy Secretary alongside such a talented team".
Mr Miliband led a more moderate party than his immediate successor Mr Corbyn, who guided Labour to its worst general election defeat since 1935.
His return comes after he found fresh popularity hosting a podcast in the wake of his 2015 general election defeat.
His predecessor in the role, Rebecca Long-Bailey, has been moved to education and joins fellow leadership rival Lisa Nandy in Sir Keir’s top team.
David Lammy, a leading voice against the Windrush scandal who practised as a barrister, was named as shadow justice secretary.
The moves will be seen as an attempt to unite a fractured party, bringing back some names from the party’s recent past while holding onto some who excelled under Mr Corbyn.
Sir Keir said: "I’m proud to have appointed a Shadow Cabinet that showcases the breadth, depth and talents of the Labour Party.
"This is a new team that will be relentlessly focused on acting in the national interest to respond to the coronavirus pandemic and rebuilding Labour so that it can win the next election."