In 1955 Marietta graduated from New York University and received a Bachelor of Science degree in Education (with great honor). In 1956 she received a degree of Master of Arts from New York University. In 1964 she graduated from École National des Beaux Arts, Paris. Also in 1980 she graduated from New York University and received a Doctor of Philosophy degree.
From 1955 to 1958 Marietta Siegel worked as an instructor at New York City Public Schools and from 1958 to 1989 at Long Island Public Schools. She held a position of an assistant professor of fine arts at St. John's University in 1965-1969. In 1970 she became an instructor of fine arts at Molloy College at Rockville Centre, New York and in 1985 at College of New Rochelle.
Since 1996 she served as a founder, exhibitions director of Stage Gallery, Merrick, New York and was a curator of 15 exhibitions.
She was a member of National Education Association, International Fund for Animal Welfare, Kappa Delta Epsilon (secretary 1954-1955) and Phi Delta Kappa.
In 1996 Marietta Siegel became a fellow at Hambidge Center Creative Arts and Sciences.
She was married to Roy F. Siegel on December 20, 1958 and had a son.