The BBC One show, hosted by comedian Rob Beckett, pitted six famous couples against each other in a series of mental, physical and emotional challenges designed to test their relationships to breaking point.
By the sixth and final episode, just three couples were left in the running - Welch and Townley, Strictly Come Dancing's head judge Shirley Ballas and her partner Danny Taylor, and comedian Stephen Bailey and his partner Rich Taylor.
They faced electric shocks and a gruelling walk over broken glass before Loose Women star Welch and her artist husband were announced as the winners.
Welch and Townley had opened up on their journey from addiction to sobriety, having met in a nightclub at a difficult time in their lives in 2011, married in 2013, and got sober together.
Welch said: "I am overjoyed, I can’t tell you. We had no doubt that we were unbreakable, but I’m just really glad to share that story with other people.
"It’s never too late to turn your life around. I love Lincoln and this is just the icing on the cake - and to have such a lovely reaction from people that you have grown very close to, it is very, very, very special."
Relationship experts Anjula Mutanda and Maria McErlane acted as judges and McErlane said: "We voted for Denise and Lincoln. Their relationship started from such a difficult beginning and they have risen like a phoenix from the flames. They are such a strong couple."
Viewers of the series had been moved by emotional moments in previous episodes that included Ballas talking about her brother taking his life, and Falklands veteran Simon Weston CBE and his wife Lucy discussing the testing times their relationship had withstood.
The Westons were back for the final, along with other stars Olympic BMX racer Shanaze Reade and her event organiser partner Teddy Edwardes, and Pimlico Plumber Charlie Mullins OBE and his singer-songwriter girlfriend RaRa.
Watch: Denise Welch met Lincoln Townley while crashing Tinie Tempah's birthday party