The Royal Canadian Mounted Police, known as the Mounties, is to allow women in uniform to wear hijabs.
Government spokesman Scott Bardsley said the move was to reflect the diversity in Canada's communities and to attract more female Muslim officers.
The iconic uniform, famed for its wide-brimmed hat, has barely changed since it was introduced two centuries ago.
Recent figures show women make up about a fifth of the RCMP but it is not clear how many this measure will affect.
Three types of hijabs were tested before one was selected as suitable for police work, local media reported.
According to the Montreal newspaper La Presse, an internal memo said the hijab could be removed quickly and easily if needed, and did not encumber officers.
Relaxing the rules
The policy was introduced quietly earlier this year, though it was not prompted by any requests from officers, according to the AFP agency.
Some 30 officers had asked for a relaxing of the rules for religious or cultural reasons over the past two years, La Presse reported.
In most cases, the requests were from male officers wanting to grow beards.
Sikh officers have been allowed to wear turbans since 1990.
The uniform, with its red serge tunic, leather riding boots and felt campaign hat, dates back to the 1800s - when mounted police were sent west to police American whisky traders.
Inspired by British military uniforms of the period, it has since only undergone minor changes.
The RCMP has become the third police force in Canada to add the hijab option after Toronto and Edmonton.
Police in Sweden and Norway, and some US states, have adopted similar policies, Mr Bardsley said.
The Metropolitan Police in London approved a uniform hijab more than 10 years ago.