After education at Giggleswick School and Manchester Grammar School, where he was academically outstanding, he did not go to a university, but went into his father's business, where he worked for 17 years. In his spare time he was a regular theatre goer, and admired and longed to emulate the critical writing of George Bernard Shaw in "The Saturday Review". In 1906 he wrote a letter about drama to a local Manchester paper. The editor printed Agate's contribution and invited him to write a weekly theatre column. After a year Agate joined the "Manchester Guardian"'s team of critics under the guidance of C. E. Montague. Even as a junior critic Agate did not hesitate to give bad notices to the leading figures of the English stage when he thought it justified. Within months of taking up his post, he wrote of Herbert Beerbohm Tree's performance as Richard II, "It was extraordinarily uninteresting, and it is amazing how badly a tragic part can fit an actor so fine as, in other directions, Mr. Tree undoubtedly is." Later, Agate was bested by Lilian Braithwaite, who responded to his assertion that she was "the second most beautiful woman in London" by replying, "I shall long cherish that, coming from our second-best theatre critic."