Swarn Singh was assaulted with a deadly weapon by Rory Benson in December 2017, according to Sikhs civil rights group The Sikh Coalition.
Singh, who maintains Sikh articles of faith including unshorn hair and a turban, had parked outside an apartment building to drop off Benson and his mother.
Benson, who was sitting in the front passenger seat, attempted to suffocate him with a piece of cloth kept in the taxi to wipe the windshield, the coalition said in a statement.
He immediately ran out of the taxi, and Benson grabbed a hammer from his bag, chasing him on-foot. Benson hit Singh in the head repeatedly, specifically targeting his turban and knocking it to the ground, it said.
He suffered a scalp laceration and a skull fracture as a result of the attack and was rushed to hospital. Benson was arrested.
The coalition said it worked with Singh for 11 months to make sure the Bellevue Police Department and the King County Prosecuting Attorney's Office were properly investigating the incident and reviewing appropriate charges.
(With inputs from agencies.)