The 16 year old, who is also managed by Bieber's pal Scooter Braun, recently performed with the Baby hitmaker on the European leg of his Believe world tour, but is currently playing his own solo dates across the U.S.
However, he has now been invited to join Bieber on the road again during his North American tour, so Simpson has axed a number of his own shows to make sure he is free.
Simpson has cancelled five dates on his Paradise tour, but will be back on stage with Bieber in Boston, Massachusetts on 20 July (13).
A statement released by the singer reads: "Being a part of the Believe Tour over the past year has been an incredible experience. It has given me a way to reach... new fans around the world and for that I am incredibly thankful to my mate Justin Bieber. I am sorry to my many fans that I am disappointing at my last five scheduled shows, however, my management team and I feel this is an important opportunity for me. I hope that my true fans understand this and are supportive of my decision. I will do my best to make it up to all of them by visiting their cities as soon as possible."
The axed dates include stops in Denver, Colorado and Detroit, Michigan.
Simpson recently treated his fans to a surprise appearance from Bieber at his solo show in Los Angeles.