Latics boss Paul Dickov hinted at the start of the week that Derbyshire would be staying at Boundary Park, after his initial loan expired last weekend.
That has now been finalised and the 26-year-old, who has scored four goals in 10 appearances since joining the Latics in September, will now remain with the League One club until December 15.
By that time he will have been at Oldham for 93 days, which is the maximum permitted under the emergency-loan system.
Derbyshire is available for the Latics' FA Cup first-round tie at Kidderminster on Saturday.
