Magness worked with Lavigne on her multi-platinum[6] debut album, Let Go, co-writing five tracks and producing 6, including "Losing Grip", Mobile, "Unwanted", "My World", and "Too Much to Ask".
[7] Prior to leaving New York for Los Angeles to collaborate with Magness, Lavigne was assigned cowriters by her label, Arista, who "failed to click with a girl who'd just discovered guitar-based rock.
"[9] Following up his collaboration with Lavigne, Magness went on to work with original American Idol winner Kelly Clarkson on her debut album Thankful.
Magness also produced five songs for another American Idol contestant, Clay Aiken, on his debut album, Measure of a Man, including the single "Solitaire", which topped the 2004 Canadian chart for 4 weeks.
Magness has either co-written and/or produced tracks for Celine Dion, Jessica Simpson, Amy Grant, Hanson, Steve Perry, O-Town, Charlotte Martin, Rachel Loy, Wild Orchid, Judith Owen, Jude, Joe Bonamassa, The Urge, Kyle Vincent, Marie Digby, Andreya Triana, Days Difference, Ill Scarlett, Ivy Lies, Christina Grimmie, Caroline Sunshine, Jermaine Jackson, Barbra Streisand, Julio Iglesias, Sheena Easton, George Benson, Patti Austin and Al Jarreau.