Reeves was schooled in both gospel and classical music, but it was vocal group R&B that caught her imagination. She began performing in the late 50s under the name Martha Lavaille, briefly joining the Fascinations and then the Del-Phis. In 1961 she joined the fledgling Motown organization in Detroit, where she served as secretary to William Stevenson in the A&R department. Her other duties included supervising Little Stevie Wonder during office hours, and singing occasional backing vocals on recording sessions. Impressed by the power and flexibility of her voice, Berry Gordy offered her the chance to record for the label. She reassembled the Del-Phis quartet as the Vels for a single in 1962, and later that year she led the group on their debut release under a new name, Martha And The Vandellas.
From 1963 onwards, they became one of Motown's most successful recording outfits, and Reeves' strident vocals were showcased on classic hits such as "Heat Wave", "Dancing In The Street" and "Nowhere To Run". She was given individual credit in front of the group from 1967 onwards, but their career was interrupted the following year when she was taken seriously ill, and had to retire from performing. Fully recovered, Reeves emerged in 1970 with a new line-up of Vandellas.