Harper, 28, ends a long-term association with Eddie Hearn’s Matchroom.
Her most recent outing was a points win against Natalie Zimmerman in Doncaster in May.
Harper has also won world titles at light-middleweight and featherweight.
With a 16-2-2 record, Harper has faced the best in boxing, including Sandy Ryan, Cecilia Braekhus, Natasha Jonas and Alycia Baumgardner.
Undisputed featherweight champion Baumgardner joined MVP this year.
Harper has been chasing a unification fight with Caroline Dubois, while MVP CEO Nakisa Bidarian said former UFC champion Holly Holm – also signed to MVP – is another option for Harper.
MVP announced this week they had signed former bantamweight world champion Shannon Courtenay.