From 2010 to 2014, Merrells achieved popularity through his role as shrewd businessman Declan Macey in the long-running ITV soap opera Emmerdale. Set in the Yorkshire Dales, Merrells' character was introduced onto the show as a new love interest for established character Natasha Wylde (Amanda Donohoe). Upon arrival, the Emmerdale website described Declan as "a shrewd businessman who knows exactly what he wants and how to get it. He's prepared to be unpopular if it's good for Business and the people in the village recognise his confidence. He does have a softer side but is not the most attentive husband in the world." At the 2011 British Soap Awards, Merrells was nominated for the "Villain of the Year" award for his portrayal of Declan, and on the show the character has had storylines surrounding the arrival of some unwanted family members including father Dermot Macey (Frank Kelly) and half-sister Megan Macey (Gaynor Faye) and his marriage to long-running character Katie Sugden (Sammy Winward) in 2012. He is the second castmember of Cutting It to also feature in Emmerdale, the other being Siân Reeves, who played Syndey Henshall in Cutting It and Sally Spode in Emmerdale. In September 2014, it was announced that Merrells had decided to quit his role after four years on the soap. Declan left the following month, going into hiding after killing his half-nephew Robbie Lawson and attempting to murder his most recent wife, Charity Sharma, whom he married earlier in the year.