The Commentary on the Mishnah has not been translated into English in its entirety. However, there are translations of Maimonides' introduction to Pirqe Aboth called "The Eight Chapters."   English translation of Eight Chapters, Introduction to Commentary on Avoth by Joseph Isaac Gorfinkle, New York: Columbia UP, 1912.

 

Maimonides’ first major work sought to give a clear, accessible and practical explanation of Jewish Law as it is laid out in the Mishnah, the first and most authoritative systematization and reorganization of Jewish Law, probably completed around 200 CE.

Online:
Hebrew translation of introduction to Commentary on the Mishnah (Da’at website)
English translation of Eight Chapters, introduction to Commentary on Avoth by Joseph Isaac Gorfinkle (New York: Columbia UP, 1912) on wikisource