"Mustang", which follows on from "moth", was directed by Anthony Minghella, the director of films including The English Patient and Cold Mountain.
The star of the 60-second spot is a convict who is transported from LA to a ranch in the desert, where, as part of their rehabilitation, the men learn to tame wild horses.
Most of them attempt - and fail - to do so by restraining the horses.
But the newcomer takes a different approach, choosing instead to set his black horse free so that he can gain its trust.
The ranch rangers then take the convict out to the desert to find the animal. When he does, it allows him to stroke it. As the convict looks into the horse's eyes, the scene changes to resemble the swirl on the head of a pint of Guinness. The endline reads: "A story of darkness and light."
The commerical, which was written and art directed by Paul Brazier and produced by The Paul Weiland Film Company, breaks on TV this week.
The target audience is drinkers aged under 35, a group that now accounts for 50 per cent of Guinness sales.
Following the release of "moth", Guinness' on-trade sales rose by 2 per cent in April and May 2004 compared with the same period last year, according to AC Nielsen. Diageo hopes to build on this growth through "mustang", which will run throughout the autumn.
Nick Robinson, the marketing director for Guinness at Diageo Great Britain, said: "This ad has all the epic drama and scale that you would expect from Guinness advertising. We have had great success with 'moth' and fully expect this ad will go down equally well with Guinness drinkers."