Prior to taking the editors job at the Daily Express, Hill was editor of Desmond's sister Daily Star title.
His journalism career spans stints on the Manchester Evening News, Oldham Chronicle, Huddersfield Examiner, Daily Mirror and People.
It is understood the 64-year-old Hill is leaving to take on new challenges.
Like rival newspaper editors he has battled falling circulations of print newspapers during his tenure.
When Hill took over in December 2003, the paper's circulation was 956,649, according to ABC figures. In December last year, it registered a circulation of 623, 689.
By comparison, rival the Daily Mail registered a circulation of 2,473,965 in 2003. Its latest circulation was 2,030,968.
During Hill's tenure, the Daily Express has been criticised in some quarters for its perceived obsession about the death of Princess Diana and its fixation with the weather.
The Express's coverage of the Madeline McCann case resulted in the paper paying £550,000 in damages to the missing girl's family.
Whittow has worked with Hill for a number of years and was previously his deputy editor at the Daily Star.
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