She was the daughter of John T. Comes and Nora W. Comes.

On Friday, October 5, 1934, she married Lieut. William Randolph Winslow at the home of her mother in Pittsburgh, Pennsylvania.

They were the parents of two children.

Marcella Comes Winslow was a native of Pittsburgh, where she attended the Carnegie School of Fine Arts. She also studied in London, Florence and Rome. She came to the District of Columbia in 1943 and lived at the same residence on P Street Northwest until she moved to the Knollwood Retirement Center. She was the official portrait painter of the United States Poet Laureate. She served as president of the District chapter of the Artists Equity Association and was vice president for the national association. She was also a member of the Corcoran Gallery of Art's Women's Commission. At her Georgetown home, she hosted writers Katherine Anne Porter, Robert Penn Warren, Allen Tate and Eudora Welty. Both Tate and Welty used her portraits on the covers of their books. Another well-known guest was Alice Roosevelt Longworth who was the daughter of President Theodore Roosevelt and the widow Nicholas Longworth III, a Speaker of the United States House of Representatives. Longworth was a fan of Anne Goodwin Winslow, the mother-in-law of Mrs. Winslow, who was a Memphis novelist. Mrs. Winslow painted a portrait of Alice Longworth in the 1960s. A 1989 article in The Washington Post Sunday Magazine detailed her experience painting Ezra Pound's portrait when he was a patient in St. Elizabeth's Hospital and her work on the portrait of Robert Frost. A 1993 exhibition at the National Portrait Gallery showcased her portraits of writers such as Frost, Porter, Pound, Tate, Warren and Welty. Frost wrote, Robert Frost, who would be willing to be remembered the way Marcella Winslow made him look in her guest book. Her portraits are found at the National Portrait Gallery, the Nimitz Library in Annapolis and the library of Eliot House at Harvard University. In 1993, her book Brushes With the Literary: Letters of a Washington Artist 1943-1959 containing correspondence with her mother-in-law was published. She died at age 94 on July 6, 2000 at Knollwood of colon cancer. She was predeceased by her husband, United States Army Colonel William R. Winslow, who died in Europe during World War II. Survivors included one son and one daughter, both of the District; six grandchildren and one sister.

Sources: The Washington Post, July 9, 2000 and Archives of American Art website.