Mirror Group Digital publisher Matt Kelly is leaving the company at the end of the month, Trinity Mirror has announced.
The company said Kelly, who has held a number of senior positions at the Mirror over the past 18 years, was 'leaving to pursue new challenges".
It added that Kelly had 'played a pivotal role in transforming both the newspaper and digital platforms'during his time with the publisher, leading the redesign of the Daily Mirror newspaper and Mirror.co.uk in 2008.
In 2009 he launched MirrorFootball.co.uk and 3am.co.uk, and again led the redesign of Mirror.co.uk in February this year.
Commenting on his departure 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."
Trinity Mirror Digital's managing director Chris Ellis, who joined the company in May 2011 from online games company IGN Entertainment, added: 'I would like to thank Matt for his huge contribution to the business, both editorially and commercially. He is a hugely creative and talented journalist and I am sure he will have a successful future in whatever he chooses to do next.'
Deputy publishing director Steve Anglesey will take on Kelly's duties until a full-time replacement is found.
News of Kelly's departure comes five months after Trinity merged its national and regional digital operations into a single unit headed by Ellis.
As part of the digital restructure, the technology behind the redesign of Mirror.co.uk is being rolled out to Trinity's regional websites this year.
The company is currently working on paid for e-editions for tablet devices for the Daily Mirror, Daily Record and its city titles.
In September 2010 Kelly announced he was leaving the business to join Perform, an online sports video business.
But two months later it emerged he was no longer leaving the group following his promotion to publisher Mirror Group Digital publisher