The new consumer campaign, created by Abbott Mead Vickers BBDO, launches on October 24 and shows BT helping an everyday family going through life's highs and lows.
Marshall stars as Adam alongside his girlfriend Jane, played by Esther Hall, who starred in the BBC television series 'Waking the Dead'.
Jane has two children, 13-year-old Joe and nine-year-old Lucy, who have all recently moved in with Adam and are adapting to their new life.
The new family will feature in television ads working across all product areas including broadband, landlines, phonebooks and 118 500.
Viewers will see Adam thrown through life's ups and downs and watch how BT can help him in various situations.
In the first spot, Adam is seen using wireless broadband on his laptop to score much-needed brownie points with Jane's children.
In the second, Adam uses his mobile to text a message to the home phone to help Joe look cool in front of his little sister Lucy.
Tim Evans, BT group marketing and brand director, said: "We wanted to connect with people as strongly as some of our great advertising campaigns of the past did -- such as with Beattie with Maureen Lipman or Bob Hoskins in 'It's good to talk' -- but in a way that's relevant to today's modern relationships."
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