Matt Piddington will appear on screen next month as a customer in the Rovers Return, fulfilling his promise to Tarmey that he would pursue an acting career.
Tarmey, who played Jack Duckworth for over three decades, passed away in November last year at the age of 71.
Piddington told the Sunday Mirror: "It would have been great if me and Grandad could have been in the Rovers at the same time but I know he was looking down from heaven smiling.
"I could feel he was with me saying, 'Go on lad I am so proud of you'. I had nerves but they felt like good nerves. I remembered all Grandad's advice, like, 'Less is more' and, 'It's all in the eyes'.
"Antony [Cotton] came over and said, 'I know you, you're Bill Tarmey's grandson'. He wished me luck and said he hoped to see me back in the Rovers full time."
Alan Halsall, who plays Tyrone Dobbs and was a close friend of Tarmey's, helped Piddington secure his role by putting him in touch with an agent who set up an audition.
Piddington has now lined up parts in ITV's Scott & Bailey and Channel 4's Hollyoaks.