Channel 4 chief executive Mark Thompson described Gardam's departure as a "big loss" for the station. Gardam joined Channel 4 five years ago,and was promoted to the role of director of television last year, after swingeing job cuts at the station that saw 200 people lose their jobs.
Of his departure, he said: "I will have been director of programmes for five years this autumn and this has always been the maximum time I thought it sensible to do the job.
"My decision is partly for personal reasons and I am announcing it now because I want to ensure there is a smooth succession and it leaves me free to consider various options without causing uncertainty here."
During Gardam's tenure, Channel 4 has seen its biggest ratings success, with the launch of 'Big Brother' in 2000. However at the same time, he has faced accusations that the station is "dumbing down". Successes during his time as director of programmes include the signing of daytime television's king and queen Richard and Judy. On the downside have been the disastrous introduction of the breakfast programme 'RI:SE' and the cancellation of the ailing soap opera 'Brookside'.
Reports say that there is no rift between Gardam and Thompson, and that the former may consider taking a part-time job at the station.
Gardam spent 20 years at the BBC, working as an editor on programmes including 'Panorama' and 'Newsnight', before leaving to join Channel 5 briefly. When Channel 4's previous chief executive Michael Jackson announced he was leaving, Gardam was named as a potential successor, with the job going to Thompson, a former colleague at the BBC.
Thompson said: "Tim warned me some time ago that he was unlikely to stay beyond 2003. He is an enormous creative force and will be a big loss."
If you have an opinion on this or any other issue raised on Brand Republic, join the debate in the .