The D company of the volunteer Ceylon Light Infantry was transformed into the Rajarata Rifles under the leadership of Lt Col (later Colonel) S.D.

On 1 October 1969 the 3rd Volunteer Battalion of the Sinha Regiment was formed at Hill School in Nuwara Eliya.

The regiment first saw action during the 1971 Insurrection and underwent an expansion with escalation of the Sri Lankan Civil War.

In 1990 the elements of the 6th Battalion successfully held the old Dutch fort of Jaffna for two months while surrounded and under siege until it was relieved by the subsequent Operation Thrividha Balaya.

The Sri Lanka Sinha Regiment is the only regiment in the history of the Sri Lanka Army to produce an army commander holding the rank of a full general (four star) and later a Field Marshal as indicated in the notable members area.