Having moved to Copenhagen to play with Geisha, in 1985 Dee joined King Diamond who were looking for additional members to complete their line-up. Dee played on the King Diamond recordings Fatal Portrait (1986), Abigail (1987), and “Them” which followed in 1988. King Diamond himself was becoming quite popular and the musicians backing him were taking a secondary role in the writing and decision making, often Diamond was the only person answering for the whole group in magazine interviews, etc. After the completion of the supporting tour for “Them”, Mikkey Dee decided to leave the band, as he felt he was becoming more of a back-up musician, rather than an equal contributing songwriter. However, he was rehired to play session drums for the recording of the band’s follow-up album Conspiracy (1989), after which he was replaced by Snowy Shaw.

While King Diamond was touring with Motörhead, Lemmy repeatedly asked Dee to join his band. In 1992 Dee accepted, replacing Phil “Philthy Animal” Taylor. On his replacement of a longstanding member, Dee said in 2006:

Dee’s first gig with the band was on 30 August 1992 at Saratoga Performing Arts Center in New York, but he did not have much input on that year’s March or Die as this had been recorded with Tommy Aldridge prior to Dee joining. He played on the albums Hellraiser and Hell on Earth, from the soundtrack for Hellraiser III: Hell on Earth.

Dee also played drums on Helloween’s 2003 album Rabbit Don’t Come Easy, stepping in for Mark Cross.

Dee played the drums for Martin “E-Type” Eriksson in the Swedish pre-qualification to the Eurovision Song Contest 2004, as well as on E-Type’s 2003 Eurometal tour.

In April 2006 King Diamond reunited with Dee at a sold-out gig at Kåren in Gothenburg, Sweden. In 2001 King referred to Dee as “one of the best [drummers] of all time and that’s something that has bothered us since he left.”

A contestant on series 1 of Kändisdjungeln on TV4 in 2009, Dee was eliminated in the 15th episode. His place was filled on a US tour by Matt Sorum, who said, “I thought either Mikkey would die in the jungle or I would die on the Motörhead tour.”

On 29 December 2015, following Lemmy’s death a day earlier, Dee announced that Motörhead had disbanded.

In January 2016, Dee joined Thin Lizzy to play on their anniversary shows. However, on 19 April it was announced that Dee would not be participating. On 28 April 2016, it was announced that Dee would be filling in for James Kottak with the Scorpions on 12 North American headlining dates, including a run of shows at the Hard Rock Hotel in Las Vegas dubbed “Scorpions blacked out in Las Vegas”. On 12 September 2016, Dee joined the band permanently.