Ciaran McCarthy was Peter Barlow's best friend in the Navy who was a cook on submarines. He arrived on the Street in 2002 and began to date Sunita Parekh. He was later arrested for going AWOL. After he was released and he returned to the area the pair got engaged; however, Sunita called off the wedding as she realised he didn't really want to marry her.
In 2004, Ciaran and Charlie Stubbs rescued Sunita and her husband Dev Alahan when were tied up in a burning Corner Shop, during a fire caused by Dev's ex-girlfriend Maya Sharma. Ciaran left the Street in 2005 after Bev Unwin made a drunken pass at him.
In 2010, Ciaran was working in a restaurant as a chef and bumped into his friend Peter again. Ciaran quit his job at the restaurant and returned to the Street with Peter's girlfriend Leanne Battersby. Ciaran found out that Peter was an alcoholic and promised to keep an eye on him but Peter caused chaos at the opening of his new wine bar. Later that year, a gas explosion happened at The Joinery where Ciaran along with Nick Tilsley helped a trapped Peter escape.
Michelle Connor caught Ciaran's eye and the two began dating. In January 2011, Michelle agreed to go with Ciaran on a cruise for several months. They returned in November for a visit and announced they were engaged, but discovered Carla's rape ordeal at the hands of Frank Foster. To help her through it, they agreed to stay in Weatherfield and Michelle took charge of Underworld whilst Carla went to Los Angeles. Ciaran found living on the street increasingly boring and to add some excitement, he gambled and lost £1,000 of their wedding money to Karl Munro and Ciaran had to think of a quick strategy to raise money for his wedding. He desperately started working as a chef at Nick's Bistro and stayed up all night preparing food for a birthday party venue in exchange for £1,100. When Nick discovered this, he fired Ciaran and when Michelle found out, he explained why he gambled their money in the first place and she agreed to leave to go back on the cruise ship with him. However, she changed her mind at the last minute and Ciaran left alone.