Mitchell-Innes was selected for the university cricket team during his first year at Oxford and made his debut against Gloucestershire. He scored his maiden first-class century in the first innings of the match which Oxford nearly won. He achieved two further centuries for Oxford that year, hitting 140 runs against the Minor Counties in a high-scoring draw, and then 171 against Surrey at The Oval. In all matches for the university that season he scored 998 runs at an average of 55.44, leading Oxford batsman that year, though Fredrick de Saram scored more runs. Mitchell-Innes won his Blue—the awarding of the Oxford "colours" to sportsmen—by appearing in the 1934 University match against Cambridge, a match in which he batted with moderate success, scoring 27 and 42 in a drawn match. In comparison to his performances for Oxford, Mitchell-Innes struggled during his eleven first-class matches for Somerset that summer: he averaged 20.93, and only passed fifty runs once, against Sussex. In the same match, he recorded the best bowling figures of his first-class career, taking four wickets for 65 runs. Mitchell-Innes' performances during the season earned him selection for the Gentlemen against Players fixture at Folkestone.