Mark Hart shared the same manager as the band Crowded House, and was suggested as a session musician for the band after their difficulties replacing keyboardist Eddie Rayner.

He contributed to Woodface (1991) as a session musician, later joining the band fully a while after Tim Finn left, and is credited as a full member on Together Alone (1993). He stayed with the band after Paul Hester left, he is seen along with Neil Finn and Nick Seymour on the promotional posters for Recurring Dream, the 1996 Greatest Hits album. Mark Hart played with the band during their farewell concert on the steps of the Sydney Opera House in November 1996. He would later join Neil Finn on stage for some of his solo concerts supporting Finn's Try Whistling This (1998) before rejoining Supertramp, producing for Tim Finn and releasing his own work (Nada Sonata, 2002).

In January 2007 Neil Finn announced that he would be reforming Crowded House with Nick Seymour, Mark Hart and a new drummer (confirmed in February as former Beck drummer Matt Sherrod), releasing a new album and embarking on a year-long world tour.

It is currently unclear whether Mark Hart contributed to the recording sessions that turned into the new Crowded House record, 'Time on Earth'.