"I don't understand why it didn't just end when Lincoln is walking down the hall and the butler gives him his hat," he said about the film, which arrived in theaters on Nov. 16.
"Why did I need to see him dying on the bed? I have no idea what Spielberg was trying to do."
The 64-year-old actor, known for everything from "Star Wars: Episodes I-III" to the iconic "Pulp Fiction," continued what the L.A. Times called a "mini-rant."
"I didn't need the assassination at all. Unless he's going to show Lincoln getting his brains blown out. And even then, why am I watching it? The movie had a better ending 10 minutes before," he said.
Spielberg, on the other hand, defended his cinematic choices and said that he didn't struggle with the ending nearly as much as with other parts of the film. "The great challenge was not how the story would end but what it would cover. Tony [Kushner's] original draft was 550 pages," he said.
The director also addressed Jackson's desire to see the shooter.
"We just knew we wouldn't show the assassination, because it would sensationalize the story. It would have suddenly focused the movie on the shooter, not the president," Spielberg concluded.
"Lincoln" stars actors Daniel Day Lewis and Sally Field, along with Joseph Gordon-Levitt and Tommy Lee Jones. It has currently been nominated for seven Golden Globe awards.