The 24-year-old performed well for the Second XI last summer, claiming 16 Twenty20 wickets at an average of 12.31 and with best figures of 3-15.
He also scored 143 runs in his only Second XI Championship appearance, with back-to-back half-centuries and a top-score of 85.
A powerful hitter and tricky leg spin bowler, McKiernan has impressed the Derbyshire coaching staff over the winter and now commits his future to the Club for the next two seasons.
Head of Cricket, David Houghton, said: “Mattie has been very committed and worked hard with the guys even though he was only initially on a short-term contract.
“His efforts and ability made it easy for us to offer him a full contract and I think he has a role to play in this squad.
“He can play as a specialist batsman but he bowls leg spin as well and he’s one of the top fielders in the side, so he offers skill in all three departments.”
McKiernan added: “I am delighted to sign a contract extension with Derbyshire. I’m thoroughly enjoying my time here and I’m looking forward to continuing my development and pushing for a place in the first team.
“Under the new coaching set up, there’s a real belief that as a newer player to the squad, I can make an impact by continuing to work hard and showcasing my ability.”
© Cricket World 2019