Unite said last week that Ms Formby’s opposition to antisemitism was “a matter of record” and she pledged to crack down on Jew-hatred in the party during her campaign to be general secretary.
She will now have responsibility for recruiting party staff, overseeing campaigns, organising annual conferences, and guarding Labour’s legal and constitutional structures.
On Wednesday, Ms Formby condemned demonstrators from the Labour Against The Witchhunt group who staged a demonstration outside Labour’s head office.
They demanded employees who were not deemed to be sufficiently left-wing be removed from the party.
The picket protesters included Tony Greenstein, who was expelled by the party last month for abusive behaviour, and Jackie Walker, who is currently suspended by Labour.