The 30-year-old was impressive during his season-long loan spell in the French top-flight last term, as he returned 11 goals in 35 appearances.
The Ivorian played a key role in helping the Violet retain their top-flight status, and he will be hoping to continue in the rich vein of form under newly appointed manager Alain Casanova next season.
"Happy to be back at Toulouse. Thanks to the president, to the supporters and to all the staff. Hoping for a better season by the grace of God," Gradel tweeted.
The winger's stint in the English Premier League was marred by injuries and, thus, restricted to 11 substitute appearances in the 2016-17 campaign.
Across his two spells with the Cherries, the 30-year-old notched 12 goals in 65 matches in all competitions.