Pending official confirmation from the two clubs, Maxi Gomes and Santi Mina will swap places, with Celta Vigo also set to receive money on top from Valencia.
Uruguay forward Gomez will move to Valencia for a fee of 14.5 million euros plus Mina, with defender Jorge Saenz also joining Vigo on loan for the season.
Mina returns to Vigo, where he got his first taste of La Liga football as a youngster between 2012 and 2015.
Valencia will hope Gomez will score the goals which they lacked last season, but Celta will also be happy with the deal.
Coach Fran Escriba now has Mina and Denis Suarez to add to his attack, while the club still have local icon Iago Aspas leading the team.