He returned to teach in Melbourne, Australia, in 1962 and subsequently became an inspector of art schools. He rose to fame when, in 1964, he won a competition to design the first decimal coinage for Australia.
In 1965, he moved to London and opened a small workshop. This marked the beginning of Devlin's own style, which often took the form of limited editions, the most popular being Easter eggs and Christmas boxes, now collectors' items. He adapted and devised new techniques to produce a wide variety of textures and filigree forms, and became well known in London's West End, producing a new collection each year. He had a prestigious showroom in Conduit Street 1979–1985.
He has designed furniture, interiors, jewellery, and commissioned pieces of all types, including trophies, clocks, centrepieces, goblets, candelabra, bowls, and insignia. Among his most popular commissions, Devlin has designed coins and medals for 36 countries throughout the world, including precious coins for the Sydney 2000 Olympic Games and the medals for the founding awards of the Australian honors system in 1975: the Order of Australia, the Australian Bravery Decorations and the National Medal.
In 1982, Devlin was granted the Royal Warrant of Appointment as Goldsmith and Jeweler to Her Majesty the Queen. He was Prime Warden of the Goldsmith's Company 1996-97. Although he is no longer Prime Warden of the Worshipful Company of Goldsmiths he continues to work with the company (as well as taking various commissions) and is particularly involved in the developing of a new institute for future Goldsmiths, and also with various other aspects which involve opportunities for up and coming Jewelers and Goldsmiths including a summer school and 'getting started' course.
Having closed his London workshop, he now works in Littlehampton, West Sussex.