The campaign, created by Bartle Bogle Hegarty, centres on the fact that up to 140,000 people die each year in situations where first aid could have saved their lives.
The ad, called 'Helpless', features a father going through the process of being diagnosed with, being treated for, and surviving, cancer.
The character dies at the end of the ad by choking on a piece of food at a barbeque, as his daughter looks on.
The ad ends with the strapline: "First aid could help prevent up to 140,000 deaths every year.
"The same number that die from cancer. Be the difference. Text 'HELP' to '84025' for a free first aid guide."
The campaign broke during last night’s 'Downton Abbey' on ITV1 and is supported by digital activity.
Media planning and buying is handled by John Ayling & Associates. PR and social media are handled by GolinHarris and St John Ambulance’s in-house team, while the campaign is searchable through the hashtag #helpless.
Scott Jacobson, director of marketing, communications and fundraising at St John Ambulance, said: "We wanted this campaign to really stun people with how needless it is for anyone to die in a situation where the most basic first aid might have saved them.
"People know that cancer is a very serious illness and take steps to prevent it and look after loved ones who are stricken with it, so we hope that the tragedy of someone surviving cancer but then dying because he needed first aid and didn’t get it will raise awareness that a lack of first aid is just as life-threatening and will motivate people to text in for a free first aid guide."
Martin Ledwick, Cancer Research UK’s head cancer information nurse, said: "Encouragingly, cancer survival rates have significantly improved over the past forty years. Research has led to better diagnosis and improved treatments, all helping to save lives.
"This campaign highlights that more people are surviving cancer than ever before but that accidents can happen at any time to anyone.
"We’re pleased to be supporting the campaign to encourage everyone to learn the first aid basics."
St John Ambulance also has a smartphone app, first aid videos, a game and workplace and community courses.
The five common scenarios depicted in the free first aid guide given away as part of the campaign are: choking, heart attack, severe bleeding, an unconscious person who is breathing and one who is not breathing.
Earlier this year St John Ambulance ran a shocking radio campaign, also created by BBH, to encourage listeners to learn first aid, featuring a voiceover artist reading an ad, before dramatically collapsing from a heart attack.Follow @loullamae_es