The 40-second TV ad will run for two months from 5 October.
The spot, which uses live action rather than Macmillan's trademark silhouettes, has been directed by John Selby from production company Upstart. Bonham Carter provides the voiceover. Three shorter versions of the ad will also be shown on satellite channels only.
In the spot, people talk about the good days they experience because of Macmillan's help. The call to action urges anyone affected by cancer to get in touch and ‘take the first step towards having more good days'.
Ali Sanders, head of brand at Macmillan Cancer Support, said: ‘This new service is a major milestone for Macmillan and will make a huge difference to people affected by cancer.
‘Our ambition is to reach and improve the lives of everyone living with cancer. Advertising is an essential tool to get the new number out to as many people as possible and to make sure they know exactly who we are and what we do.'
Press ads with the slogan ‘Good day?' and ‘Bad day?' will appear in national newspapers and consumer magazines with online banner ads appearing on sites such as AOL, Yahoo!, MSN and Zylom.
Arthur London is behind the creative, while PHD and i-level are handling the media buying. Outside advertising space across the UK has been donated.