[2] In response to a decision by the State Government to provide secondary education to children living in the Adelaide suburbs,[3] Unley High School (then Unley District High School) was founded in 1910[4] as one of four secondary institutions established for this purpose.

[3] Initially it was housed[4] and under the control of the Headmaster of the Unley Primary School but was operated by "special staff" who carried "on the secondary work".

After complicated negotiations, a trust associated with the school eventually acquired a block of land and a cottage.

(1931: 956 students, 1934: 638, 1939: 869) Unley High had been a coeducational school from the beginning, but in fact, most classes were taught in single sex groups.

In some of the darkest days of World War II the Parents and Citizens Association was founded and had its first meetings.

Land at Netherby, part of the old Peter Waite bequest for agricultural education was finally made available for a new Unley High School.

With another secondary school, Mitcham Girls Technical High, beginning to occupy the Kyre Avenue site, a decision was taken in 1965 to shift all students to the Netherby campus.

One of Unley High's most significant teachers, Jim Giles, was temporarily in charge of the school.

The Environment Group helps to increase the sustainability of the school, while decreasing the negative impact it has on the earth because of energy consumption, water usage and waste.

Recent achievements include the purchase of a 24,000-litre rainwater tank to replace the water used in the hand basins and showers in the Life Be In It Gym, the purchase of solar panels on the roof of the school, a water grant to replace all the toilets in the school with dual-flush toilets, and an intensive recycling program.