The actress, who had a Weatherfield guest stint as David Platt's girlfriend Zoe Willson last year, is to play a troublesome teenager named Roz in the Yorkshire-based drama.
According to The Sun, Roz will be introduced to the serial as a friend of student Holly Barton (Sophie Powles).
A source said: "Teen drug-dealing in Emmerdale might seem unthinkable but drugs are a problem in villages too.
"The storyline will be handled responsibly and the outcome will show the damage that drugs do, especially to teenagers."
As well as Coronation Street, Porter has previously appeared in Doctors, Shameless and Ashes To Ashes.