The 28-year-old will have his contract bought out by Nottingham Forest without a fee being paid and is travelling to the Midlands to conduct his deadline day medical.
The Belgium international was not part of Thomas Tuchel's plans at Chelsea and has not been included in any matchday squad for their first five games of the season.
Batshuayi is now part of a remarkable summer of spending for Steve Cooper's newly-promoted side who have spent more than almost any team in world football - barring Chelsea and a few others.
It ends a six-year spell after Chelsea spent £33million to sign the striker from Marseille, after which he spent most of his time as a back-up option to Diego Costa or Tammy Abraham before a series of loan moves away.
Excelling at Borussia Dortmund but not hitting his usual heights at any of Valencia, Crystal Palace or Besiktas, he had mixed fortunes away from Stamford Bridge.
At his peak, the Blues rejected several big-money permanent offers from Dortmund and demanded £50million.
Batshuayi departs with the legacy of scoring the goal that won Chelsea's last league title in 2017, with his close-range strike confirming the Blues as champions under Antonio Conte.