Mitchell has been named vice-president, UK affiliate sales and business development, as well as vice-president, commercial, digital media.
In the UK sales role, she will manage the company's distribution negotiations for Discovery content across all platforms.
As vice-president, commercial, digital media, she will work with Discovery Networks International's digital teams in London and Silver Springs, US, to develop digital offerings.
For the past two years, Mitchell has been vice-president, international strategy and mergers and acquisitions for Discovery Networks International.
Before that, she spent four years working with MTV Networks in a number of commercial roles.