Rosita Hamiton was born in 1955 in Brooklyn, New York. Her mother and maternal grandmother moved from Guaynabo, Puerto Rico to New York in the early 1950s. Her father grew up in Guánica, Puerto Rico and moved to New York City when he was young.
Rosita Hamilton spent her childhood and young adult years in the Bushwick neighborhood of Brooklyn. Her mother worked as seamstress and participated in the International Ladies' Garment Workers' Union. Her father was a member of the International Brotherhood of Teamsters (IBT). Hamilton attended St. Barbara’s Roman Catholic School and then St. Michael’s High School.
She went to Queens College, eventually earning her bachelor’s degree in 1986. She was active in the women's movement, joining the National Organization for Women (NOW) in 1972, and in the anti-Vietnam War movement. She began her teaching career at Catholic schools in New York City. After moving to New Jersey, she taught at St. Helena in Edison and then spent the rest of her career teaching history at Linwood Middle School and in the high school in North Brunswick. She was a member of the New Jersey Education Association (NJEA).
Since retiring in 2016, she has stayed active in the women's movement and in organizations such as Indivisible and the ACLU. Currently residing in Monroe Township, she previously lived in Piscataway and South Brunswick.