Douglas, who is currently in a senior role at Universal Music UK, is to take over from Carolyn Reynolds, who has held the chief executive position at Lime and its forerunner Mersey Television for six years.
Reynolds will now work on new projects for All3Media, the parent company of Lime Pictures, while also retaining a consultancy role at Lime.
Douglas joined Universal as managing director of commercial media partnerships and TV projects in 2008 following her departure from Radio 2 in the wake of the "Sachsgate" scandal involving Jonathan Ross and Russell Brand.
She oversaw the growth of Universal's television output, including reality series Popstar to Operastar, a co-production with ITV Studios and Renegade for ITV1.
Universal will continue to work with Douglas as part of a co-production deal that will see Lime becoming its exclusive partner for all music-related content. Lime will also now use Universal for music in all its TV projects.
Douglas, who will start at Lime in the New Year, said: "I have loved developing music formats with (Lime creative director) Tony Wood and Lime over the past few years.
"The opportunity of working more closely still across the portfolio, while also ensuring that Universal's programming is in safe hands, was an opportunity I simply could not turn down.
"To successfully capture the imagination of the youth market is a difficult job but Lime Pictures has the hearts and minds (as well as the remotes and browsers) of the UK's youth audience."
Speaking about the Lime co-production deal, Universal Music UK chairman and chief executive David Joseph said: "This is an ambitious new partnership for us and I'm delighted that we will continue to benefit from Lesley's expertise and talent when she takes up her new role."