After joining radio station 3DB, he moved to television to sister station HSV-7 in early 1970 as a reporter. One of his first assignements at HSV-7 was to go to Darwin to report on the devastation of Cyclone Tracy that ripped through the tropical city on Christmas Day 1974.
In 1987, Walden was sacked by new management after HSV-7 was taken over by the Fairfax group, and was told of his dismissal just minutes before going on air to present what became his final news bulletin.
A week later, Walden joined the Eyewitness News team at ATV-10 as a reporter and presenter of the segment Mal's Melbourne, presenting human interest stories. Walden continued as relieving newsreader, reporter and weekend newsreader at ATV-10, as well as presenting special events such as Young Australian Of The Year and ATV-10's 30th Anniversary.
In 1996, he took on the role of chief newsreader after David Johnston announced his move to HSV-7. He was appointed newsreader of the station's 5pm newscast alongside co-anchor Jennifer Hansen. He celebrated 30 years in television news on 8 June, 2000. In 2004, he published a detailed history of ATV-10 to commemorate the stations upcoming 40th anniversary. He now co-anchors the news alongside Helen Kapalos.
Mal is married to Pauline, and has twins James and Sarah who are 23. James is currently being treated for Hodgkin's Lymphoma.
Mal is a keen gardener and he enjoys golf.