Complex sentence: Cronin began his literary career as a contributor to "Envoy, A Review of Literature and Art", was Editor of "The Bell" in the 1950s and Literary Editor of "Time and Tide" (London).
Split into simpler sentences: Cronin began his literary career as a contributor to "Envoy, A Review of Literature and Art". He was editor of "The Bell" in the 1950s and literary editor of "Time and Tide" (London).