Jim Downer was born in the Isle of Wight, and he lived there until the family moved to Leeds in 1935. He was educated at Woodhouse Grove School, followed by five years studying painting at the Leeds College of Art. In 1951, he won the annual travelling scholarship, which allowed him to spend five months in Italy, during which time he walked from Rome to Venice.
The following year, he spent four months as a harpooner of basking sharks off the Atlantic island of Achil, using rowing boats called curraghs.
In 1952, he moved to 18 Rugby Street in London, and under the tutorship of Monty Reed, he learned the skills of designing and producing exhibition stands. He then joined John Wilkins, shopfitting manufacturers and who were designing London's first supermarkets.
In 1959, he joined the BBC as an exhibition designer, with the purpose of enhancing the public's understanding of the corporation's role, while the Pilkington Report was being produced. The following year he married Wendy Barbara Craft, a film editor. In 1961, he invented and had produced by Dunlop, the first flat running Travelator for a BBC exhibition in Charing Cross underground station, and this went on to become used all over the world.
He then set up his own private practice design office in Islington which continued until 2001. Here he designed and produced exhibition stands, showrooms, graphics, trademarks and print for clients that included British Coal, British Telecom, Culham Fusion Laboratory, Glaxo, the Radiochemical Centre, Plessey and the UK Atomic Energy Authority.
For the 29 years between 1969 and 1998, Jim and Wendy owned and sailed around European and West Atlantic waters in a 32ft sailing trimaran called Sea Finches. He has been a widower since 2003, and continues his photography and sculpture in the Isle of Wight, to which he returned to live.