Born at 20 Newstead Street in The Avenues, Kingston upon Hull, in 1903, Mackaill lived with her father, who owned a dance academy, after her parents separated when she was around eleven years old.

This she did at the Thorne Academy of Dramatic Art and Dancing in Wigmore Hall, attending the first year of a two-year course before leaving to start her paid career.

[7] She met a Broadway stage choreographer who persuaded her to migrate to New York City at 17, where she became active in the Ziegfeld Follies, dancing in his Midnight Frolic review.

[9] In the following years, Mackaill would appear opposite such popular actors as Richard Barthelmess, Rod La Rocque, Colleen Moore, John Barrymore, George O'Brien, Bebe Daniels, Milton Sills and Anna Q.

[10] Mackaill rose to leading-lady status in the drama The Man Who Came Back (1924), opposite rugged matinee idol George O'Brien.

Her most memorable role of this era was the 1932 Columbia Pictures B film release Love Affair (1932) with a then little-known Humphrey Bogart as her leading man.

[14] Mackaill lived at the luxurious Royal Hawaiian Hotel on the beach at Waikiki as a sort of celebrity-in-residence and enjoyed swimming in the ocean nearly every day.