Mackenzie, who was most recently chief executive at 123WebTV, an online search engine providing access to video and TV programmes, will now lead LoveFilm's digital activity as well as head up its expanding streaming services.
Her appointment comes as the widescale deployment of IPTV is creating new possibilities for LoveFilm's subscription-based streaming services in the UK and Europe.
Mackensie was previously interim chief executive of Kangaroo, the online joint venture project between BBC, ITV and Channel 4 which failed to make it past the Competition Competition last year. Mackenzie had previously worked for News Corporation with Tata Sky in India and BSkyB in the UK.
Simon Calver, chief executive at LoveFilm, said: "Lesley's experience in the digital market is second to none. The next 12 months are going to see further exciting developments in LoveFilm's streaming expansion and we are thrilled to have Lesley at the digital helm working alongside the existing great talent we have in this area."