Sabine Sinjen was born on August 18, 1942 in Itzehoe and grew up with her mother, the journalist Marlen Sinjen, née Kolbe, in Hamburg and Munich. In 1957, at the age of 15, she made her film debut in the socio-critical drama "Die Frühreifen" produced by Artur Brauner. One year later she played one of the students of a strict Prussian girls' boarding school in "Mädchen in Uniform" ("Girls in Uniform") alongside Lilli Palmer and Romy Schneider. Also in 1958, she took on her first leading role - as in "Die Frühreifen" directed by Josef von Baky - in "Stefanie", which was a huge success, made Sinjen a teenage star and spawned the sequel "Stefanie in Rio". 

Her image as the natural, unspoiled young girl with the "touching earnestness" was cemented in Heimatfilms such as "Die Försterchristel" and in a number of other CCC productions by Artur Brauner. In the early 1960s she also appeared in Helmut Käutner's "Das Glas Wasser" ("A Glass of Water", 1960) and in the German western "Die Flußpiraten vom Mississippi" ("The Pirates of Mississippi", 1963). At the same time, she began to focus on theater and television productions, appearing at the Schiller Theater in Berlin (1961-63), the Staatliche Schauspielbühnen Berlin (1967), and the Theater in der Josefstadt in Vienna (1967-71). She became popular on television as the daughter of a veterinarian in the ARD TV series "Alle meine Tiere" (1962-63).

In the mid-1960s, Sabine Sinjen succeeded in changing her image with leading roles in Ulrich Schamoni's "Es" ("It", for which she received the German Film Prize as Best Actress), "Alle Jahre wieder" ("Next Year, Same Time"), and "Wir - zwei" ("We Two", Ernst-Lubitsch-Award for Sinjen), in all of which she portrayed women confronted with profound problems in their everyday lives. In these productions of the Young German Cinema, a bourgeois relationship or marriage no longer appeared as the goal of all dreams, but as the cause of ever new questions. In the 1970s, Sinjen, who co-signed the campaign "Wir haben abgetrieben!" ("We've had an abortion!") in Stern magazine in 1971, also continued to celebrate successes as a stage actress, making guest appearances at the Zurich Schauspielhaus, among other venues, and was a member of the ensemble at Hamburg's Thalia Theater from 1976 to 1980. 

In 1984 she became seriously ill with a carcinoma of the lacrimal glands, and in 1986 she went blind after an operation on her right eye. Shortly before, she had played the role of Caroline Friedrich in Peter Schamoni's documentary film "Caspar David Friedrich. Grenzen der Zeit" ("Boundaries of Time: Caspar David Friedrich") in which she played the role of Caroline Friedrich.

In December 1987 she made a highly acclaimed theatrical comeback at Berlin's Schillertheater in Jean Cocteau's one-woman play "The Human Voice". Film and television roles became rarer and her last big screen appearance was in 1993 in "Das Haus im Ginster" ("The House in the Macchia").

On May 18, 1995, Sabine Sinjen died of cancer in Berlin at the age of only 52.