Hollywood stand-in, scene painter, and interior designer, Shields had been Haines' casual pick-up in New York in 1922. Billy Haines fell in love with his stand-in, and they moved in together in 1923, and this led to a 50-year long relationship.

Shields followed Haines to Hollywood and stayed with him despite the star's promiscuity, and through his rise and fall in Hollywood.

In 1930 Billy Haines and Jimmy Shields bought an antique shop and developed their interest in interior design by giving free advice to their Hollywood customers and friends.

In 1933 the MGM boss Louis B. Mayer told Billy Haines that he had to choose between his gay lifestyle or his career. Billy Haines chose to stay with Jimmy Shields. Louis B. Mayer terminated his contract and ensured that he could not work in the film industry again.

Their lives were disrupted in 1936 when members of the White Legion wearing hoods to hide their faces, dragged them from their home and beat them because a neighbour had accused the two of propositioning his son. Ultimately Shields and Haines chose not to report the incident to the police.

After moving to Malibu their business prospered until their retirement in the early 1970s. Their many clients, in addition to hundreds of Hollywood celebrities, included and Ronald and Nancy Reagan while Reagan was governor of California, and Walter Annenberg while he was the U.S. Ambassador to England.

Shields and Haines remained together for the rest of their lives despite numerous infidelities. The relationship between the two men, referred to as "the happiest married couple in Hollywood" by their friend Joan Crawford, ended only with Haines' death from cancer in 1973; Shields, who suffered from what may have been Alzheimer's Disease put on Haines' pajamas, took an overdose of pills, and died the following year.

His suicide note read: "It's no good without Billy". They were interred side by side in the Woodlawn Memorial Cemetery.