Young Cassidy is based upon the autobiographical writings of firebrand Irish author Sean O'Casey. Rod Taylor is Cassidy, a boisterous boy who digs ditches to support his mother (Flora Robson) and sister (Sian Phillips). In his spare time, Cassidy is active with the Irish revolutionary movement against the occupying British. He still finds time enough for romance, notably with trashy chorine Julie Christie (in her first major role) and timid librarian Maggie Smith. Cassidy's latent writing talents are encouraged by such Irish literary giants as W.B. Yeats (Michael Redgrave) and Lady Gregory (Edith Evans), and in typically expeditious Hollywood fashion Our Hero almost instantly becomes a Man of Letters. John Ford began the direction of Young Cassidy, but fell ill and had to relinquish his responsibilities to Jack Cardiff; even the most diehard auteurist will have trouble discerning the personal "signature" of either director.
~ Hal Erickson, All Movie Guide