Mothercare made the appointment after seeing creative presentations from St Luke's, Miles Calcraft Briginshaw Duffy and Rapier. Mother and TBWA\London were involved in the initial stages.
Anna James, the marketing director at Mothercare, said: "We are now in a position where we can be confident about updating the look and feel of the Mothercare brand."
St Luke's has been tasked with developing a customer communications strategy for Mothercare, which will include a television campaign. The first work is not expected to break until autumn.
St Luke's executive creative director, Al Young, said: "We are delighted to be given the opportunity to work with such a fantastic brand. It is a terrific fit for us and we can't wait to start playing our part in the turnaround programme."
In October, the retailer created a senior marketing role to focus on more effective consumer targeting as a precursor to a return to advertising.