Michael Stephen Portnoy was born April 20, 1967 in Long Beach, New York. His father was a DJ so Mike was exposed to many different bands growing up, such as Queen, Led Zeppelin, and The Beatles, all of whom he would later name as having influenced him. He taught himself to play the drums and was involved with many local bands, eventually being awarded a scholarship to Berklee College of Music in Boston, Massachussettes. It was there that he met John Myung and John Petrucci and formed the band Majesty, which would later become Dream Theater.

Mike is also a recovering alcoholic. He is in the midst of writing a 12 part suite for each of the 12 steps of the AA recovery program. He has written 4 songs encompassing the first 9 steps so far ("The Glass Prison", "This Dying Soul", "The Root of All Evil", and "Repentance").

In addition to Dream Theater Mike is a collaborator on many projects. His first and arguably most successful collaborative effort was Liquid Tension Experiment with Jordan Rudess, John Petrucci, and Tony Levin. He has also worked with OSI, Neal Morse, and Transatlantic in addition to many tribute bands honoring Rush, Led Zeppelin, The Who, and The Beatles. He has also filmed many instructional videos, the most recent being In Constant Motion.

Mike is an avid collector (especially of Dream Theater memorabilia), and he loves watching movies in his spare time. He currently resides in Pennsylvania with his wife Marlene, their daughter Melody, and son Max.