Music was a natural part of Gunnar Michaeli's childhood. His mother, for example, sang in a radio choir. Gunnar got his first musical experience at an early age. "I guess I started playing piano when I was tall enough to reach the keys of my mother's piano." Then he was 5 years old. He started composing his own songs when he was 8 years old, and when he played them, his parents recorded them on tape. One night he couldn't sleep, so his mother let him stay up to watch TV. That's when he heard Alice Babs perform the Beatles song "Yesterday". "Mom told me that the song was originally done by a pop band and I asked her if she could buy me that record." So she bought him the Beatles album Oldies but Goldies. The Beatles became his first idols, and in 1971 he bought the album Let It Be and learnt how to play some of the songs.

Gunnar liked to play in the forest, where he hid his cigarettes and porn magazines, and at one time even started a forest fire! "I tried to play soccer and hockey, but soon I had to realize my limitations." When he was in the third grade in school, he and a friend used to play covers in the schoolyard. Gunnar played the guitar and his friend played the tambourine. Gunnar took guitar and piano lessons at the public music school in Upplands Väsby for one or two years. "Boring, but still useful. At least the guitar lessons." He started his first band when he was 14 years old. "I played the guitar because I couldn't afford to buy a synthesizer. So I played the guitar through an old radio, and it sounded terrible. I sang too, and that sounded even worse. There was a couple of neighbors who actually moved!" 

When he was 15 years old, he bought his first synthesizer and one year later, he formed his first serious band, Ictus. Both Ictus and his next band, Acri, were strongly influenced by symphonic rock. After Acri split up, he played in different bands until he formed a new band, Avalon. "We sounded like a heavier version of Toto and we recorded a couple of demos." In 1983 Avalon played on a rock festival which also featured EUROPE on the bill. In 1984 Gunnar joined the band Universe, which was just about to go in the studio, when EUROPE approached him and asked him to join the band for their Wings of Tomorrow tour. At first he was only hired as a background musician, but after the first leg of the tour was completed, the band asked him if he wanted to be a permanent member. "I contemplated whether I should join since I had my own band. I also wrote songs. We were gonna make it and become really big! But in the end I came to the conclusion that I could give it a try. And to come from a hole outside Stockholm and go out on tour, that's where you wanted to go! It wasn't my band, but I got into it really fast."

When he joined EUROPE, he still stuck to his real name, but for the second leg of the Wings of Tomorrow tour he decided to take the artist name Greg Michaeli. "I was stupid enough to try and find a name that sounded 'coool'. Now, a really cool name in English would be Gunnar." Later on he decided to go for a different name: Mic Michaeli. After a jam session Mic and Joey Tempest co-wrote the ballad "Carrie", which was included on the third EUROPE album, The Final Countdown. During the recording of that album in 1985, Mic found out that his girlfriend, Mia was pregnant. She gave birth to their first son, Marcus in 1986, making Mic the first EUROPE member to become a father. In the same year Mic played on Tone Norum's debut album, One of a Kind, which was produced by Joey. John Norum and Ian Haugland also played on the album.

After EUROPE went on hiatus in 1992, Mic started to work as a producer for artists like Paulo Mendonca. He also participated in the blues project Walking Heads, together with Kee Marcello among others. In 1994 Mic, John Levén and Ian Haugland joined Glenn Hughes for his From Now On..."album and tour, which resulted in the live album Burning Japan Live. In 1995 Mic and Ian joined Brazen Abbot and played on their first album, Live and Learn, before John Levén joined the band in 1996. With Levén in the lineup, Brazen Abbot recorded the albums Eye of the Storm in 1997, Bad Religion in 1998 and Guilty as Sin in 2003. Mic, John and Ian also played on Thore Skogman's album Än Är Det Drag in 1998, Nikolo Kotzev's Nostradamus in 2001 and Last Autumn Dream's self-titled debut album in 2003. Mic and Ian also played with blues guitarist Tommy TC Carlsson, Sha-Boom and the Deep Purple/Whitesnake cover band White Purple. Mic co-wrote three songs on Joey Tempest's third solo album, Joey Tempest, which was released in 2002, and in 2007 he played on the Bosses Vänner album Läget? Mic made a guest appearance on John Norum's seventh solo album, Play Yard Blues, which was released in 2010.

Mic is currently living in Stockholm. He has three children with his ex-wife Mia Hertler, Marcus, Moa and Mathilda. Marcus made a guest appearance in the music video for "Hero", the second single from EUROPE's sixth studio album, Start from the Dark.