Siegel was described by The New York Times as "a director of tough, cynical and forthright action-adventure films whose taut plots centered on individualistic loners".

In 1945, two shorts he directed, Star in the Night and Hitler Lives, won Academy Awards, which launched his career as a feature director.

He made the original Invasion of the Body Snatchers (1956), described by The Guardian in 2014 as a "fatalistic masterpiece" and "a touchstone for the sci-fi genre" which spawned three remakes.

[5] For television, he directed two episodes of The Twilight Zone, "Uncle Simon" (1963) and "The Self-Improvement of Salvadore Ross" (1964), and was the producer of The Legend of Jesse James (1965).

[6] He worked with Eli Wallach in The Lineup, Elvis Presley and Dolores del Río in Flaming Star (1960), with Steve McQueen in Hell Is for Heroes, and Lee Marvin in the influential The Killers (1964) before directing five of Eastwood's films that were commercially successful in addition to being well received by critics.

These included the action films Coogan's Bluff and Dirty Harry, the Albert Maltz-scripted Western Two Mules for Sister Sara, the American Civil War melodrama The Beguiled, and the prison-break picture Escape from Alcatraz.

Siegel had a long collaboration with composer Lalo Schifrin, who scored five of his films: Coogan's Bluff, The Beguiled, Dirty Harry, Charley Varrick, and Telefon.

He worked as a dialogue coach on four additional Siegel films: Private Hell 36 (1954), An Annapolis Story (1955), Invasion of the Body Snatchers (1956), and Crime in the Streets (1956).

In Charley Varrick starring Walter Matthau (a film slated for Eastwood, but ultimately turned down by the actor), he has a cameo as a ping-pong player.