Baker initially joined Vitesse, with whom the Blues have an agreement to loan players, at the beginning of last season.
The 21-year-old made 31 appearances in the Dutch top division to help the Arnhem outfit to a ninth place finish.
And the England youth international, who was instrumental in the victorious under-21 side at the Toulon Tournament this summer, is delighted to have the chance to establish himself under new manager Henk Fraser.
"We are pleased that we Lewis have convinced yet to come out a year for Vitesse,” Allach said.
“The qualities of Lewis are known to us
“As a next step in the pleasant cooperation with Chelsea, we welcome Lewis for a second season.”
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