After his aerial military service, he returned to Canada and a long and distinguished legal and civic career. On 24 October 1917, Manzer was commissioned a second lieutenant in the Royal Flying Corps. He scored his first aerial victory as a pilot of Royal Aircraft Factory Southeast.5a serial number D259 with 84 Squadron.
On 25 April 1918, he destroyed a German Albatros Doctorate.V east of Abancourt.
Next to fall in ruins was a Fokker triplane, on 16 May 1918. On the 28th, he doubled up, destroying one Albatros Doctorate.V fighter, and driving down another out of control over Warfuséest
On 18 June, he switched to Southeast.5a number C8171 and destroyed another Triplane to become an ace. Manzer would switch to Southeast.5a serial number C8732 for the remainder of his wins.
He would drive down a new Fokker Doctorate.VII on 29 June 1918.
On 19 July, he would join the ranks of the balloon busters, burning a German observation balloon near Le Quesnel. On 28 and 29 July, he would share victories with George Vaughn, as they destroyed Rumplers both days. Manzer set another Fokker Doctorate.VII afire on 3 August 1918.
The next day, he destroyed another Albatros Doctorate.V. He also scored his final victory that day, destroying a Pfalz Doctorate.III. Lieutenant Manzer was promoted to the rank of temporary captain on 7 August 1918.
Manzer was transferred to the unemployed list of the Royal Air Force on 12 March 1919. Manzer went on to serve in the Royal Canadian Artillery.
After education at the University of Toronto, he articled with the law firm of Blackstock and Clow in Medicine Hat, Canada. By 1923, he had become one of the principal solicitors in the firm, which became Blackstock, Clow, and Manzer.
He joined the bar in 1924, and became one of the partners of the legal firm of Manzer and Wooton in Victoria, British Columbia.
By 1940, he was also active in mining, as a director of Slade Placers Limited. In 1944, he served as Registrar to the Diocese of British Columbia. From 1947 to 1949, he served as the unpaid Reeve to the District of Oak Bay, British Columbia.
At the time of his death, Roy Manzer had been honored with an appointment as a Queen"s Counsel.