The series of ads, created by Dye Holloway Murray, bore statements such as: "Dear Gordon Brown, I can save you £508 million a year. Please call me on 020 7147 9980. Many thanks, Polly Tommey."
The spot, aimed at raising the profile of The Autism Trust in the lead up to National Autism Day, successfully prompted Gordon Brown to arrange a meeting with Tommey.
The billboards went up on 23 March and Brown responded four days later.
As well as a phone call, he sent a letter to the charity stating: "I'm a bit busy this week, however my health advisor Greg Beales, Phil Hope the minister for care services and Elaine Hill the Department of Health's autism advisor will meet me in the mean time to talk about the work of the autism trust."
Brown then acknowledged the devastating impact of autism, saying: "I understand that people don't get the support they need and deserve and we therefore want to do more to provide this support."
Since sending the letter, the PM's office has arranged a meeting on 15 April at Downing Street with Tommey, herself a mother of an autism sufferer, as well as scheduling further meetings in the future.
Speaking about the campaign, which spanned 78 billboards, all given for free, Tommey, said: "It's been an unbelievable response.
"I've had to got through the stage of putting billboards up to get myself heard - our campaigning before has fallen on deaf ears.
"But it's been more than successful we've got a meeting at Downing Street"