Throughout the years, Marcello played in various bands such as Stetson Cody Group, Norbom Hilke and Noice, before he formed Easy Action in 1982. They released two albums, Easy Action and That Makes One. Easy Action was the first Scandinavian band to sign a World Wide major label deal with a US label, with the Warner label "SIRE" in 1983. Zinny San later left the band and was replaced by Tommy Nilsson. They recorded "That Makes One" 1985/1986 and released it in 1986, only months before Marcello left the band (in November 1986) to join Europe, replacing their first guitarist John Norum. Marcello had previously collaborated with Europe vocalist Joey Tempest on the hugely successful single "Give A Helpin' Hand" for the charity project Swedish Metal Aid. Marcello produced the platinum selling record and subsequently gave Tempest his very first hit single. The success of this collaboration was probably instrumental for the decision of asking Marcello to become the new guitar player. When he joined Europe in 1986 the band previously hadn't done any extensive touring outside Sweden, but that was about to change when "The Final Countdown" eventually reached number one on the singles charts in 25 countries. In 1987 Europe embarked on their first world tour; "The Final Countdown World Tour". In 1988 Marcello recorded his first studio album with Europe; Out of This World, at the Olympic Studios in London. Later that same year they embarked on the "Out Of This World Tour", which started off with a US leg together with Def Leppard. Ex Thin Lizzy keyboardist Darren Wharton's group Dare supported the band on the European leg of the tour. Marcello, whom 1987 together with the rest of the band emigrated to the Caribbean in an attempt to escape the then ferocious Swedish margin tax, was spending most of his time in Los Angeles when not in Providenciales on Turks And Caicos Islands. The writing and preproduction of the next album took place in LA and San Francisco. It was recorded in 1990/1991 at Enterprise Studios in Burbank, California. Prisoners in Paradise was released in 1991 and shortly after they embarked on the "Prisoners In Paradise World Tour". After the tour the band decided to go on hiatus in 1992.
In 1993 Marcello and former Easy Action drummer Freddie Von Gerber collaborated in the band Red Fun, and released a self-titled album that featured a melodic metal sound with heavy blues influences. In 1995 Marcello released his first solo album Shine On, in the singer/songwriting tradition and therefore a take off from his previous work. During 1997-2001 Marcello produced and wrote/cowrote songs for various artists in his own studio; "GEM Studios" in Gothenburg, Sweden. Namely Canadian band The Moffats number one hit single "Bang Bang Boom", the title song for R&R Hall Of Fame inductee Percy Sledge's 2004 album Shining Through The Rain, and 3 consecutive platinum albums for Swedish singer Pandora in Japan. He also did several guest appearances as a guitar player, (like on the1999 In Flames album Colony, contributing the second guitar solo on the song "Coerced Coexistence".)
In 2003 he released the album Melon Demon Divine under the project/band name Kee Marcello's K2. The power trio consisted of Ken Sandin, bass and Snowy Shaw, drums. Over the following years of touring the band went through some member changes, with the exception on of bass player of Ken Sandin, who is in the band to this day. When Europe reunited with John Norum later that year, Marcello decided not to be part of the reunion. "I told them I didn't want to participate in a [new] studio album because musically, I want to go in a different kind of direction than the music Europe stands for," he said in an interview, "Then we talked for a while about doing a six-piece tour – it didn't turn out that way because of different reasons." However Marcello also made it clear he's happy that Europe reformed and are touring without him. "I think it’s really great that the guys are travelling around playing all those songs to a lot of happy fans."
Easy Action reunited for a gig at the Sweden Rock Festival in 2006 and rereleased their debut album Easy Action with some previously unreleased live recordings. Kee Marcello's K2 toured extensively all over Europe and the East during 2008-2009. In 2009 Marcello signed a management deal with Gerry Helders (TMS Management), and started working on two new albums, due for release 2011/2012. He also became an endorsee of Gibson Guitars that year.
After having more that 2.000 appliances, Marcello and TMS Management put together an audition for members to his new band in London November 2010. The band have been doing showcases at Midem in Cannes, France, and ILMC in London, and will embark on their first tour in 2011.