McDonald first gained fame as a member of the Doobie Brothers, where he served as the band's lead vocalist and keyboardist from 1975 to 1982. During his time with the Doobie Brothers, McDonald's soulful voice became a defining element of the band's sound.

After leaving the Doobie Brothers, McDonald embarked on a successful solo career, releasing a series of albums that showcased his distinctive voice and songwriting talents. Some of his most popular songs include "I Keep Forgettin' (Every Time You're Near)," "Sweet Freedom," and "Yah Mo B There," a duet with James Ingram.

McDonald's music is characterized by its smooth soul and R&B influences, as well as his distinctive baritone voice. He continues to tour and perform, and his music remains popular with audiences around the world.