The Senegal international is the Blues' second summer addition after signing a long-term deal at Stamford Bridge.
The Senegalese striker is the Blues' second acquisition under new manager Mauricio Pochettino and has committed to a long-term deal at Stamford Bridge.
It is understood Villarreal will receive more money from Chelsea than his €35 million release clause, but this will be done in numerous installments.
When Bournemouth and Jackson reached an agreement on a deal in January, Jackson was on the verge of heading to England, but the transfer fell through after he failed a physical.
Jackson became more of a star at Villarreal after this move fell through, scoring nine of his 12 La Liga goals in the final eight games.
