After a 'technical' issue seemed to have scuppered the signing of the 27-year-old midfielder on loan from Bolton Wanderers, the deal was announced on the Nottingham Forest midfielder on Saturday morning.
And Trotter made an immediate debut at home to Ipswich Town, scoring in the 95th minute to earn a second 1-1 draw of the week for Dougie Freedman's side at the City Ground.
In form Sheffield Wednesday are next up at Hillsborough on Saturday.
Elsewhere in the Championship, Saturday brought another managerial casualty as Charlton parted company with head coach Guy Luzon after a 3-0 home defeat by Brentford.