After a year teaching English at Berlitz Language School in Barcelona, he returned to London to study at the Royal College of Art from 1953 to 1956, where he met Peter Blake, Joe Tilson, Len Deighton, Denis Bailey, David Gentleman and Dick Smith.
[2] He married Paola Biagi, an Italian national, in 1956 (they met with a heated discussion about if orange and pink were a good or bad colour pair).
He visited Robert Brownjohn, Ivan Chermayeff and Tom Geismar in New York, became friends with Bob Gill, and was commissioned by Leo Lionni to design a cover for Fortune magazine in 1958.
An early product was their 1963 book Graphic Design: A Visual Comparison in John Lewis's Studio Paperbacks series.
Two new partners joined, and the partnership evolved into Pentagram in 1972, with Forbes, Crosby, Kenneth Grange and Mervyn Kurlansky, with clients including Lloyd's of London and Daimler Benz.
Fletcher also wrote several books about graphic design and visual thinking, most notably The Art of Looking Sideways (2001), which had taken him 18 years to finish.
An exhibition of his life's work was displayed at the Design Museum in London between 11 November 2006 until 18 February 2007, alongside the posthumous publication of a book, Picturing and Poeting.