Two years after leaving Stamford Bridge on a high after his heroics helped them win the Champions League, the emotional pull of reuniting with manager Jose Mourinho proved too great a draw for the Ivory Coast striker.
"It was an easy decision - I couldn't turn down the opportunity to work with Jose again," the 36-year-old told the club website (www.chelseafc.com).
"Everyone knows the special relationship I have with this club and it has always felt like home to me."
Drogba's last appearance for Chelsea came in the 2012 Champions League final against Bayern Munich, where he almost single-handedly clinched the trophy for the London club, scoring the winning penalty in the shootout after powering home a header to force extra time.
It seemed a fitting way to end his eight-year spell at Stamford Bridge where his dynamic game, combining power and pace, almost reinvented the traditional target-man role.
Drogba joined the Blues from Olympique Marseille for 24 million pounds ($40.8 million) in 2004, at the start of Mourinho's first spell in charge, and scored 157 goals in 342 appearances, hoovering up silverware along the way.
He won three Premier League titles, four FA Cups, two League Cups as well as the Champions League before leaving in 2012.
While Chelsea's billionaire owner Roman Abramovich seemed determined to bring more glamorous centre forwards to the club, with Andriy Shevchenko and Fernando Torres all arriving with lofty reputations, the Ivorian proved immovable.
He remains their record scorer in European competition with 34 goals while his nine strikes in nine cup finals is also a record.
When he left Stamford Bridge two years ago to play for Shanghai Shenhua in China, many thought his career was on the wane with his performances in that final season fluctuating between brilliant and largely ineffective.
Mourinho has decided to bring him back, however, after a successful year in Turkey playing for Galatasaray that showed he still had something to offer at the highest level.
The Portuguese predicted in March, when Galatasaray played Chelsea in the Champions League, that Drogba would one day return to the Chelsea family and said on Friday that there was no emotion or sentiment involved in the decision.
"He's coming because he's one of the best strikers in Europe," Mourinho said.
"I know his personality very well and I know if he comes back he's not protected by history or what he's done for this club previously. He is coming with the mentality to make more history."