The veteran presenter announced in June he would be leaving the role after 25 years in the presenter's chair.
When he announced his departure, Mr Dimbleby said he would be returning to his first love of reporting.
He said: "At the end of the year I will have been chairing Question Time for a quarter of a century and I have decided that this is the right moment to leave.
"It has been a privilege to work for a programme which brings voters face to face with those in power. I am grateful to the production teams and to the BBC who have made this possible.
"Instead, after years in the studio, I now plan to return to my first love: reporting."
The 80-year-old first presented Question Time on 14 January 1994 and is the longest serving presenter of the show, which was one of the BBC's most tweeted about programmes of the year.
During his BBC career, Mr Dimbleby presented political programmes such as Panorama and chaired many debates, including the party leaders' debates in the run-up to general elections since 2010.
He has been the BBC's anchorman for all general elections since 1979 and presented the broadcaster's coverage of the first referendum in Europe, a role he repeated in 2016 for the BBC's coverage of the EU referendum.
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