The France Under-20 defender's contract expires at the end of the season, enabling Barca to snap him up on a free transfer. It is believed a number of clubs, Manchester City among them, were keen to nab Todibo.
Widely regarded as one of the best defensive prospects in Ligue 1, Todibo has made 10 league appearances for Toulouse this season.
The 19 year-old wrote on Twitter: "I am very happy to have signed for Barcelona from July 2019.
"It is more than a club and I thank them for their trust in me.
"It will be a new stage in my young career and I will put all my determination into achieving great things.
"In the meantime, I remain a Toulouse player and am available to help my team-mates as long as I remain under contract.
"Toulouse have allowed me to grow and discover Ligue 1 and I will be eternally grateful. Thank you."
Although Todibo is one for the future, he could quickly emerge as a first-team player with Gerard Pique now 31 and Samuel Umtiti and Thomas Vermaelen suffering with frequent injury problems.