MacLachlan was born in Harlem, New York; her mother, Iris South MacLachlan, and father, James MacLachlan, were both Jamaican-born members of the Church of the Illumination. Attending P.S. 170 and Julia Ward Junior High School, MacLachlan graduated from Julia Richmond High School in 1950. She received a bachelor's degree in psychology from Hunter College in 1955. She then worked as an executive secretary in New York City before turning to acting. She later performed at the Tyrone Guthrie Theatre in Minneapolis.
A one-time contract player for Universal Studios, MacLachlan made her debut in two episodes of The Alfred Hitchcock Hour in 1965. She appeared in episodes of The Fugitive, The Invaders episode "The Vise as Mrs Baxter" (1968), The Girl from U.N.C.L.E., Star Trek, Ironside, and The Mod Squad. She also appeared in the films Uptight (1968), Change of Mind (1969), ...tick...tick...tick... (1970), Darker Than Amber (1970), Halls of Anger (1970), Sounder (1972), The Man (1972), Tightrope (1984), Murphy's Law (1986), The Boy Who Could Fly (1986) and The Thirteenth Floor (1999).
MacLachlan also won a Los Angeles-area Emmy for her performance in KCET's Voices of Our People: In Celebration of Black Poetry in 1981. She would later serve as grant committee chairman for the Academy of Motion Picture Arts and Sciences.
Suffering from cardiovascular disease in her later years, MacLachlan died from complications from the condition on October 11, 2010 at the age of 77 at Kaiser Permanente Medical Center in Los Angeles. She is survived by a daughter, Actress Samantha McLachlan. MacLachlan resided in the Silver Lake neighborhood of Los Angeles.
