In 1927 Llewellyn became a member of the Edmonton Art Club and in 1931 one of the original members of the Alberta Society of Artists. A selection of his paintings were accepted that same year at an annual juried show at the National Gallery of Canada. In 1934 he moved to London where he established a temporary residence, showing in the Royal Academy's annual exhibition.

In the same year he was accepted to exhibit by the Royal Society of British Artists. He then set up a studio in the Montparnasse section of Paris and his “Autumn on the Seine” was exhibited in the Societe Nationale des Beaux-Arts. His success continued with pictures being accepted by the Salon d’Automne.

Invited as a top representative of Canadian landscape painters, Llewellyn was commissioned alongside members of the Group of Seven, AY Jackson, AJ Casson and Edwin Holgate, by the Canadian Pacific Railway.

Petley-Jones was represented by the Dominion Gallery in Montreal. In 1955 he was commissioned by the Alberta Government to paint portraits of Queen Elizabeth and the Duke of Edinburgh for the Alberta Legislative Building.