Bheki Ntshalintshali stays on as Cosatu General-Secretary, and Solly Phetoe will continue to serve as his deputy.
Losi will be the first woman to lead the trade union federation, which is holding its 13th National Congress in Midrand in Gauteng.
Outgoing Cosatu President Sdumo Dlamini had announced that the elections agency will announce the name of the new office-bearers.
Later on Tuesday, the General-Secretary of the South African Communist Party (SACP), Blade Nzimande, is expected to address delegates.
Cosatu and the SACP, together with the ruling ANC, make up the tripartite alliance.
– African News Agency