The appointment comes as Sir Philip Green shakes up the management ranks at Arcadia and its parent Taveta.
Gallagher is the face of the high street retailer’s fall look book, Casely-Hayford has done tailoring for the brand.
Man will mount a group runway show held on June 10 at The Old Truman Brewery.
Topman continues to support MAN, together with Fashion East.
This is the second time the designer has collaborated with the high street label.
Joint committee will be hearing testimony from BHS advisers, Arcadia principals.
The images shot by the Comme des Garçons protégé were styled by the Topman team.
Grace Wales Bonner, Phoebe English and Kiko Kostadinov were added to the lineup for spring.