Abidal joins the newly-promoted Ligue 1 side on a one-year deal, but the club will have the option of offering him an extra year when the current deal expires.
The 33-year-old France international has been a free agent since June after Barca decided against offering him a new contract.
Abidal's career has been heavily interrupted in recent years due to illness.
He underwent surgery to remove a liver tumour in March 2011 but made a rapid recovery and was playing again before the end of the same season and started the UEFA Champions League final against Manchester United that year, which Barcelona won 3-1.
However, in March 2012 it was announced Abidal needed a liver transplant, which he underwent in April of that year and kept him out of action for just under 12 months.
He returned to training last December and made his long-awaited comeback on the pitch as a substitute in a league match with Real Betis at the Nou Camp in April, and went on to make a total of five appearances for Barcelona in the final two months of the season.
The Frenchman began his professional career with Monaco in 2000, spending two years there before joining Lille.
He announced he had returned to the club with a message on his official Twitter account, which said: "I am very happy to have returned to France and Monaco, where it all began for me."
Abidal, who was unveiled at the Stade Louis II stadium today, is the latest of a growing list of notable captures by the French principality club this summer, which includes Radamel Falcao, James Rodriguez, Ricardo Carvalho, Jeremy Toulalan and Joao Moutinho.