Variety mentions that his initial Broadway appearance was in Paul Potter's stage adaptation of Ouida's popular historical romance, Under Two Flags, starring Blanche Bates, which opened at Garden Theatre on February 5, 1901, and closed in June.

Continuing to perform in numerous other short films (virtually all productions of the early 1910s were between one and three reels in length), the following year he joined filmmakers' exodus to the newly formed West Coast motion picture mecca of Hollywood.

Seen in at least eight films in 1912, he made twenty-six in 1913 and sixteen in 1914, with six of the 1914 titles extended to feature length, including the five DeMilles, in first of which, The Man on the Box, a comedy-drama released in July, he had a prominent supporting role as a character named Count Karloff.

Forty years old in 1916, Johnston enjoyed a brief period as a mature leading man, second-billed to such stars as the "Sweetheart of American Movies", Mabel Taliaferro, in God's Half Acre, and twenty-two-year-old Norma Talmadge in Fifty-Fifty, which cast him as her wealthy husband.

There were two more appearances for Cecil B. DeMille, in 1939's Union Pacific and 1942's Reap the Wild Wind but, in contrast to his stature in 1914, Johnston, now in his sixties, is barely glimpsed in fleeting unbilled bits.