Born in Montreal, Canada, Haylett moved with his parents back to Britain at the age of two and was brought up in Southend-on-Sea. He studied art there and at St Martins, London. A recent correspondent (2016) writes that she owns a portrait by Haylett which the artist painted of her father during the war (1944) while they were posted to India. He was primarily a portrait painter although he had a broad range of art and design skills, and was invited to St Ives shortly after the War by his friend the photographer Gilbert ADAMS.

He was so taken by the ambience of the town that he took a studio in Westcott's Quay on the spot. His fiancée Jean, a fashion student, joined him and they married in 1946. His favourite portrait subject was his wife, although he soon began to win commissions from the rich and famous. He was asked by one of the organisers of the Daily Mail Ideal Home Exhibition to submit a design. His scheme was selected for the 1954 Exhibition and was such a success he was given the accolade of being selected the following year as well.

He also redesigned a number of shops in St Ives, was a design consultant for Plymouth Breweries, and designs for two of his homes were featured in Ideal Homes. Haylett also taught art at Redruth School of Art, the St Ives School of Painting and Camborne College.

In August 2011 an auctioneer selling one of his paintings came across a businesss card giving Haylett's address in 1950 as 'The Warren, St Ives'.