Pellizotti has raced at Pro Continental level with Androni Giocattoli-Sidermec since 2012 but previously rode with Nibali at Liquigas from 2006 through to 2010.
Pellizotti had vowed to quit the sport in 2011 when he was handed a two-year ban for irregular blood readings stemming from his UCI Biological Passport. After a lengthy case, which was appealed by the UCI, the Court of Arbitration for Sport ruled that he should lose his 'king of the mountains' title from the 2009 Tour de France, as well as his podium place in the 2009 Giro d'Italia. He was also handed a fine of 115,000 Euro.
Since his return to the sport, the Italian has carved out a captain's role at the Androni team, winning the national road title in 2012 and finishing 10th at the Giro d'Italia in 2013.
"He was third overall in the 2009 Giro and he won the polka dot jersey in Paris as the best climber of the Tour de France in 2009," the Bahrain-Merida team announced in a press release.
Pellizotti, who turns 39 in January, added: "I am really happy for more than one reason.
"I will race another season and above all with Bahrain-Merida pro cycling team I will return to the WorldTour, which means riding with top cyclists in the world, like Nibali. What makes me even more excited is the idea to be part of a new team, to share the enthusiasm of a new beginning with my co-riders and to feel everyone's desire to achieve something good together. It is the same feeling I had in 2005 with Liquigas, where I also met Vincenzo, [Enrico] Gasparotto and many members of the current staff of Bahrain-Merida."
Pellizotti's programme is yet to be announced but, given his experience and his ability, he is likely to work alongside Nibali throughout the season.
"It's amazing how now I can support him toward his goals, among which is the Giro d'Italia, where he will be aiming for this third victory," he added.