The appointment is part of a strategy to strengthen the agency's creative output and management team.
In his new role, Timms will work alongside Paul Walton, the agency's head of art, to strengthen creativity.
He replaces Shaun Moran, who was made the creative director in September last year.
Timms is one of the most-awarded copywriters in the business. Recent accolades include the Grand Prix at the 2004 DMA Awards for Star Alliance.
In 2002, his hitchhiker mailing for the AA's breakdown service won the Grand Prix at the first Lions Direct at the Cannes Advertising Festival.
During his five years at HTW, Timms has been responsible for award-winning work for M&G Investments.
Steve Aldridge, the creative partner at Partners Andrews Aldridge, said: "We've had a really good year and Stephen joining will strengthen our creative skills further."