In 1893, Vallack tied for first place when he graduated, after winning the Arts Faculty's Levey and Renwick scholarships in 1890, from the University of Sydney with a Bachelor of Medicine and Master of Surgery. In 1896 he went to the United Kingdom to further his studies, returning to take up his medical practice in Bowral in 1898. He moved to Sydney in 1911. Apart from his private practice, he was also a consultant at Royal Prince Alfred Hospital and the Mater Hospital at North Sydney. With the outbreak of war in 1914, he was made a captain in the Australian Medical Corps on home service, fulfilling his army duties, private practice and hospital duties throughout the war. Throughout his life he was an active sportsman, playing A grade football, golf, tennis, was noteworthy in athletics, and winning a cricket blue at university. Vellack also conducted for the Bowral Music Club. He wrote medical articles and an internationally recognised text Principles and Practice of Asepsis (1905), but turned to literary works in later life, writing poetry and a play. His obituary in the Sydney Morning Herald (9 June, 1930, p.6) says that he also wrote a book which "may be published posthumously". This work was not traced.
