Sin Min High School started as a primary school. The first Principal was Mr Yap Fun Hong(1945-1949). With the help of Mr Heng Chin Soo and Mr Tan Choon Teng, they set the school on 1 November 1945 to educate the rural Chinese in the area.
The original school was made up of three rented bungalows at Upper Serangoon Road.
620 students were registered in October.
In 1956, it became an aided school with both primary and secondary classes. Students of the school participated in the anti-colonial struggle. Many of the brighter ones went on to Nanyang University.
In 1986, Sin Min High became an English-medium school. In 1990, the school shifted from the 5th Milestone Upper Serangoon to Hougang Avenue 8 and was renamed Xinmin Secondary School.
The current location at Upper Serangoon Road is occupied by Helping Hand, a Christian half-way house for the rehabilitation of ex-drug addicts.