North will be responsible for leading Freeview's integrated marketing campaigns and developing the marketing strategy for Freeview's portfolio, including on-demand service Freeview+ and high-definition offering, Freeview HD.
He will be charged with defining a new brand positioning for Freeview, with a view to deepening viewer engagement and building on its British heritage.
Leach, also a former BBC marketer, resigned less than a year after being appointed to the role last June.
In April, Freeview parted ways with its creative agency 18 Feet & Rising, which chose not to repitch for the £10m account. North will play a part in selecting a new agency, with the shortlist including Leo Burnett, The Red Brick Road and Wieden+Kennedy.
Ilse Howling, managing director at Freeview, said: "Guy's wide-ranging industry experience will be invaluable, as Freeview continues to find new ways to engage with viewers about the most-watched content and best-loved features it has to offer.
"Guy will play an important role in developing the relationship between viewers and the Freeview brand for post-switchover era and ensure our mass market proposition remains dynamic and competitive in a connected world."
North will report to Howling when he joins Freeview on 27 June. He will work closely with Freeview operations director Gill Hind and strategy director Liz Reynolds, and will sit on the Freeview board.
In his marketing career, North has worked across a wide variety of businesses, most recently at charity Victim Support as executive director of marketing with responsibility for marketing, communications and fundraising.
North worked at the BBC for 10 years until March 2009. He held a number of senior marketing roles, including head of marketing for the BBC TV channel portfolio and head of global superbrand development at the BBC's commercial arm, BBC Worldwide.
After starting his career agency side, North moved to alcoholic drinks producer Bass Brewers in August 1991, where he held various marketing roles for drinks brands, including Carling, Grolsch and Worthington.
Freeview is jointly owned by its five shareholders, the BBC, BSkyB, Channel 4, ITV and Arqiva, and offers free-to-air digital TV channels, radio stations and interactive services, through an aerial.