A reported £1 million budget has been earmarked to support a national press campaign promoting spring and summer styles for the company's K Softees range.
The assignment, awarded on the basis of strategic recommendations from three competing shops, is the first for Senioragency in the UK since it was set up last year as a joint venture with Mitchell Patterson Grime Mitchell.
The standalone operation was set up to target the UK's over-50s market, which now numbers 20 million people.
The appointment ends the arrangement under which K Shoes' creative work has been produced in-house following a split with Walsh Trott Chick Smith.
Universal McCann will continue to handle media.
K Shoes, famous for its television advertising through Bartle Bogle Hegarty in the early 90s, is now targeted at the mature market by its parent company, C & J Clark International.
Jo Passmore, the K Shoes marketing manager, said: "Senioragency's contribution has helped us focus our ideas, and the K Softees campaign will make a key contribution to the future development of the K Shoes brand."
Chris Mitchell, who runs Senioragency in the UK, commented: "Our task is to portray the brand in a more relevant way to the lifestyles of the over-50s market."