Åkerfeldt is known for his progressive rock-influenced songwriting style and his frequent use of both clean tenor and growled vocals. On stage, he is notably interactive with audiences, frequently eliciting laughter with his dry humour and giving anecdotes between songs.
A native of Stockholm, Mikael Åkerfeldt was the vocalist for Eruption, a death metal band which he formed in 1988 at 14 years old. After Eruption came to an end in 1990, he joined Opeth, ostensibly as a bassist. When vocalist David Isberg insisted Åkerfeldt join the band, all other members left. Isberg assumed guitar duties, and when he left Opeth two years later, Åkerfeldt replaced him as the vocalist. Åkerfeldt performed the death vocals on Katatonia's album Brave Murder Day and Sounds of Decay EP.
On 15 August 2003, Mikael Åkerfeldt married his longtime girlfriend, Anna Sandberg. On 13 September 2004, Anna gave birth to a daughter whom they named Melinda. The couple had their second daughter, Mirjam Ebba Maria Åkerfeldt, on 28 October 2007.
Mikael Åkerfeldt revealed in September 2009 that he is contemplating recording a singer-songwriter acoustic solo album.  However, in 2014 he expressed the view that he didn't have the need of a special solo project and that he can put pretty much anything into Opeth. 
Mikael Åkerfeldt with Opeth at Ruisrock 2008 in Turku, Finland.
Åkerfeldt uses 3 different tunings: E Standard, Drop D and Open D minor 9 (D-A-D-F-A-E). He has almost exclusively used PRS guitars since the Deliverance/Damnation era and has his own signature model.
Dream Theater: Åkerfeldt performs a spoken word part in "Repentance" on their 2007 album Systematic Chaos. He also sang the second verse of the same song on its first and to date only live performance, during the Progressive Nation 2008 tour. He also performed the growled verse of their song "A Nightmare to Remember" with the band live.
Ihsahn: Åkerfeldt performs on the song "Unhealer" from the 2008 album angL.
OSI: Åkerfeldt performs lead vocals on the track "Stockholm" for OSI's 2009 album, Blood.
Porcupine Tree: Åkerfeldt sings backing vocals on "Deadwing", "Lazarus", "Shesmovedon" and "Arriving Somewhere But Not Here" and plays a guitar solo on "Arriving Somewhere But Not Here" on the 2005 album Deadwing.