Born in Reading, Stanley was first apprenticed to a house decorator whilst in his spare time painting with house paint on card. First winning a Scholarship to Reading University, he further studied at the Allan Fraser Art College, Arbroath, Scotland. He travelled to America but returned in 1914 to serve in the Armed Forces. In 1915 he married Bertha Drew (1892-1975), who had encouraged his artistic ambitions, and with whom he had had a  child, Gilbert, in 1911. The marriage may have been prompted by his enlistment, but he was discharged from his military duties in 1916.

In 1922 Stanley and Bertha, while holidaying in Cornwall, discovered Lamorna. He gave up a teaching post in Reading, renting 'Lily Cottage', and there they remained. Gardiner was encouraged and heavily influenced by Samuel John Lamorna BIRCH, for whom he made frames (and for Stanhope Forbes and others) when finances were tight. Gardiner worked often in the open air, and in the studio he built for himself (Bludor Studio).  He studied at the FORBES SCHOOL in 1926, and showed at NAG in Christmas Exhibition of that year. His titles included Sun Daisies, April Morning, Lamorna, etc. He also took pupils for lessons in the open air, carrying on the long-held plein air tradition.

He maintained his artistic contacts in Reading and London, exhibiting with the Reading Guild of Arts and at a number of London galleries.

A major treasure at Penlee House, Penzance is A Portrait of Stanley Gardiner painted in 1938 by the artist Richard Copeland WEATHERBY (Seal), that was shown first at STISA and then hung at the RA in 1945.  It depicts Gardiner 'who stands, legs astride, palette in left hand, brush to the fore, facing his easel with the Lamorna Quay in the background.' (D Bradfield)