The New York Police Department said the turbans must be navy blue and have the NYPD insignia attached.
Under the new rules, religious members of the force are also permitted to grow beards up to half-an-inch long.
Sikh officers have until now worn turbans under their caps. Beards have not been permitted.
New York Police Commissioner James O’Neill said the change was to encourage religious members of the community to apply “to work in the greatest police department in the nation”.