Having worked in other towns, Mullions arrived in Timaru in 1904 and rapidly developed a strong practice. He was well supported by prominent families in the district, for both residential work and commercial buildings. Many buildings remain.
Presumably in pursuit of new opportunities Mullions moved away, finally to Auckland, where he entered in to partnership with Sholto Smith. Smith was born in France then lived in Canada before migrating to New Zealand as a young architect in 1920. The two architects flourished in partnership. They produced many notable buildings particularly houses in the Arts and Crafts style and many larger buildings including the Shortland Street flats – now well protected. Their houses in Epsom, Parnell and Remuera are also gaining in status now that Aucklanders are keen to retain heritage fabric. Of note is a picturesque house in Parnell, La Morna which is very similar in style to a house in Chalmers Street Timaru designed by Mullions some years earlier. This is the Arts and Crafts style two-storeyed house located alongside the carpark of the Highfield Village Mall.
History will record Thomas Coulthard Mullions (1878-1957) as an exceptionally talented architect who provided a significant body of work to both Timaru and Auckland. Research is under way by an Auckland author to bring this story to publication.