They had been without a labour contract since May 2019.
After voting to strike on May 11, the parties held four intensive but productive negotiation sessions.
The details of the agreement will be revealed at an upcoming general assembly where members will be asked to vote to ratify the agreement.
The Public Service Alliance of Canada is one of the largest unions in Canada. It represents more than 200,000 workers in many fields across the country and around the world. In addition to its headquarters in Ottawa, the PSAC has 23 regional offices.