Mirror Group Digital publisher Matt Kelly is leaving at the end of this month.
Media website journalism co.uk reports that Kelly, who has worked for the company for 18 years, is departing to pursue 'a couple of very exciting new opportunities'.
Kelly said; "I've had the most blessed 18 years and the privilege of working with an extraordinarily talented team. I am incredibly proud of everything that we have achieved together.
"But I have a couple of very exciting new opportunities ahead of me and I know the Mirror is in terrific hands. It feels like the perfect time to move on."
Confirming his departure, Trinity Mirror said Kelly "has played a pivotal role in transforming both the newspaper and digital platforms", having been the lead on the Mirror website and newspaper redesign in 2008 and was also involved in its latest site redesign earlier this year.
He also helped launch MirrorFootball.co.uk and 3am.co.uk in 2009.
Last week Trinity Mirror announced that following the relaunch earlier this year and the company's "investment in digital resource" digital revenues had grown by 12.5% in the first half of this year.
Its nationals division, including the Daily Mirror, Sunday Mirror and The People, was also said in the interim report to have "performed strongly in the period with operating profit increasing by 11.8 per cent". Overall the company reported a rise of more than 20% in pre-tax profit.
Steve Anglesey, deputy publishing director, will take on Kelly's role until a full-time replacement is found.