An advocate of method acting, Dennis was often described as neurotic and mannered in her performances; her signature style included running words together and oddly stopping and starting sentences, suddenly going up and down octaves as she spoke, and fluttering her hands. Walter Kerr famously remarked that she treated sentences as "weak, injured things" that needed to be slowly helped "across the street." Nonetheless, William Goldman, in his book The Season, referred to her as a quintessential "critics' darling" who got rave reviews no matter how unusual her acting and questionable her choice of material. Kerr said the following during Dennis' stint in Any Wednesday: "Let me tell you about Sandy Dennis. There should be one in every home."
Her last significant film role was in Come Back to the Five and Dime, Jimmy Dean, Jimmy Dean (1982).
Dennis died from ovarian cancer in Westport, Connecticut, aged 54.
| Year | Film | Role | Other notes |
|---|---|---|---|
| 1961 | Splendor in the Grass | Kay | |
| 1966 | Who's Afraid of Virginia Woolf? | Honey | Academy Award for Best Supporting Actress; Nominated - Golden Globe |
| 1967 | Up the Down Staircase | Sylvia Barrett | |
| The Fox | Jill Banford | ||
| 1968 | Teach Me! | ||
| Sweet November | Sara Deever | Nominated - Golden Globe | |
| 1969 | That Cold Day in the Park | Frances Austen | |
| A Touch of Love | Rosamund Stacey | ||
| 1970 | The Out-of-Towners | Gwen Kellerman | |
| 1974 | Mr. Sycamore | Jane Gwilt | |
| 1976 | God Told Me To | Martha Nicholas | |
| 1977 | Nasty Habits | Sister Winifred | |
| 1981 | The Animals Film | Herself | |
| The Four Seasons | Anne Callan | ||
| 1982 | Come Back to the Five and Dime, Jimmy Dean, Jimmy Dean | Mona | |
| 1988 | Another Woman | Claire | |
| 1989 | Parents | Millie Dew | |
| 976-EVIL | Aunt Lucy | ||
| 1991 | The Indian Runner | Mrs. Roberts | |