CHICAGO—David Coleman Headley was sentenced to 35 years in federal prison Thursday primarily for his role in planning the 2008 Mumbai terrorist attacks that killed more than 160 people, including six Americans.

Mr. Headley, a Pakistani-American, pleaded guilty to 12 terror-related counts in 2011. In exchange for cooperating with U.S. and Indian authorities, American prosecutors didn't seek the death penalty, and instead recommended 30 to 35 years in prison.

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