DeMarchi played keyboard, bass and did some of the production and engineering work for the 1994 Freddy Curci Dreamer's Road album.

DeMarchi supported O'Riordan on keyboard and as backing vocalist at the award ceremony at Midem 2008, Cannes, France – 27 Jan 2008.

The Orange County Register's Entertainment Section review of the Cranberries concert printed that "Demarchi triggered the swelling orchestration and provided welcome background support all evening by bolstering the sound and enriching vocals.

"[7] Variety reported that "The Band, augmented by keyboardist-guitarist Denny DeMarchi from O'Riordan's recent solo disc No Baggage, brings sufficient energy to the set, the influence of the Smiths quite prevalent; oddly enough, the more racket they created, the more cohesive they sounded.

DeMarchi accompanied Dolores O'Riordan in a Live performance on CBC Radio in Toronto Ontario Canada.

[11] Dolores O'Riordan joined guest host Jesse Wente live in Studio Q to talk about her second solo album release, No Baggage, and the reunion of the Cranberries with plans for a world tour in mid November 2009.

Aside from being an experienced multi-talented musician, DeMarchi has also shown a keen interest in audio engineering and music production projects.

[12] DeMarchi was also the keyboard and rhythm guitar player on this album, which was released by an English record label Z-Records on 22 October 2012.

He has started recording work, whenever time permitted, on a small portion of his portfolio of songs and has released 10 tracks on his MySpace profile's music player.