When Mary Thompson was asked whether she was proud to bear her famous brother's name, she replied, ""Yes I am, but that pride is duly kept under control by the great pain which such talent caused both to him and to us."" John Walsh's biography is a verification. His painstaking correlation of the facts and phases of Thompson's life with his poetry, a life he interprets as ""what he deliberately and ruthlessly made it--a vehicle for poetic achievement""--might equally prove Thompson's lack of control. Thompson was dismissed from the seminary as lacking a vocation as a priest, but Walsh proposes it was due to another vocation, that of the poet. When he failed his medical examinations, Thompson was already a drug addict; addiction bounded him the rest of his life and left the cause of his death (morphomania? tuberculosis? both?) in doubt. Walsh does not associate the addiction with Thompson's ""remarkable power of imagery;"" The Hound of Heaven, for which he is known today, and in which he achieved ""the ultimate expression in the long tradition of cosmic imagery,"" was written in a recuperative period. He traces influences, literary and life experiences, draws from and refutes the Meynell biography. Beyond his works, liberally quoted, there is little from the reclusive Thompson himself. Sympathetic when he cannot be admiring, Mr. Walsh provides the only full biography currently available (besides the Butler, London House book). Notes.