The campaign, created by The Romans, seeks to show how powerful simple acts of kindness can be, particularly around Christmas.
The text is 7.5km long and painted next to the yellow line along platforms, running the length of the Virgin Trains route from London to Glasgow.
It is being rolled out along the Virgin Trains West Coast route, with the film’s message of goodwill painted across station platforms that include London, Birmingham, Liverpool, Manchester, Preston, Carlisle and Glasgow, appearing over 14 nights in 14 locations in total.
The platform text will include online links to simple ways to intervene when someone is struggling with poor mental health.
The 1946 film It’s a Wonderful Life is widely viewed as an uplifting Christmas staple, but it also deals with the difficult story of one man’s struggle with a life that hasn’t gone to plan.
James Fletcher, head of corporate partnerships at Rethink Mental Illness, said: "It is vital at this time of year to let people know that help is available if they need it. We have worked closely with Virgin Trains for the last two years to help raise funds so that more people can access support in communities along the West Coast network. This campaign highlights the need for this support at a time of the year which can be difficult for some of us, and we are proud to be part of it."
Throughout December, customers will also be able to watch It’s A Wonderful Life on Beam, Virgin Trains’ on-board entertainment service. Volunteers from Rethink Mental Illness will be fundraising at Virgin Trains stations throughout the campaign period.