The Primera Division club announced that Keita, pending a successful medical, will pen a contract tying him to Los Che until the summer, with the option of a further season after that.
Valencia added that the 34-year-old Mali international is due to arrive in Spain later today to put the finishing touches on his move.
A club statement read: "The midfielder Seydou Keita, subject to a medical, will sign with Valencia until June 30, with the option of a further season more.
"The Mali international, who had played at Chinese Super League club Dalian Aerbin until December 31 of last year, will arrive this afternoon at 1635 (local time) at the Manises airport."
Keita started his career in France with Marseille, Lorient and Lens before moving to La Liga with Sevilla in 2007.
He spent one season with the Andalusian club before Barca paid a reported 14million euros to take him to the Nou Camp.
During four seasons at Barca, the midfielder won a host of trophies, including three Primera Division titles, two Champions Leagues and two Copa del Reys, before leaving the Catalan club in 2012 to join Chinese outfit Dalian.
He had one year left on his contract at Barca but activated a clause that allowed him to leave should he not start more than half of Barca's fixtures in the previous season.
Valencia are 10th in the Primera Division standings on 25 points, 11 adrift of the top six.
Meanwhile, Valencia have also announced that three of their first-team squad - Helder Postiga, Andres Guardado and Dorlan Pabon - are set go out on loan.
A club statement read: "Valencia have reached an agreement for the loan of Dorlan Pabon to Sao Paulo, through to June 30th, 2015. The Colombian striker has passed a medical for the Brazilian club and has already begun training with his new team.
"Deals have also been reached, pending the relevant medicals, for the loans of Helder Postiga to Lazio and Andres Guardado to Bayer Leverkusen, with both agreements holding an option to buy at the end of the current season.
"Postiga and Guardado have today travelled to Rome and Leverkusen, respectively, to undergo their medicals with the permission of Valencia."