Leonard was born in Crystal Falls, Michigan. He entered the music Business with late 1970s Chicago-based pop rock band Whisper, then later the same band membership, Trillion (name changed for legal reasons), featuring Future Toto singer Dennis "Fergie" Frederiksen on lead vocals. His early career also featured short stints as a keyboardist in Frank Zappa’s band in 1976 and The Allman Brothers Band in 1980.
He went on to act as musical Director and lead keyboardist for the Jackson Victory Tour in 1984.
His work with Madonna includes her albums True Blue (1986), Who's That Girl (1987), Like a Prayer (1989), I'm Breathless (1990) and Ray of Light (1998). He scored her 2008 documentary I Am Because We Are, played keyboards with her at Live Aid (1985), and was musical Director and keyboardist on The Virgin Tour (1985) and the Who's That Girl World Tour (1987).
In 1997, Leonard released the instrumental album Rivers on his own record label, Unitone. Leonard has three children: a daughter Jessica, a Writer (for whom Madonna's song "Dear Jessie" was written), and two sons, Sean, who is a musician, and Jordan, a projection mapper and VJ under the name Pickels Visuals.
More recently Leonard has collaborated with Leonard Cohen, acting as a Writer and Producer for 2012’s Old Ideas and 2014’s Popular Problems, and co-writer, co-producer of 2016’s You Want It Darker. "Nevermind," a song from Popular Problems that Leonard co-wrote and produced, was featured as the title theme for Season 2 of HBO's True Detective. Speaking of Patrick in 2016, Cohen remarked that, "He is such a magnificent Composer. I don’t think there’s anybody working today with those kinds of skills."