A Cardiff Blues academy product, Harris began his career as a prop, making the switch to hooker during his time at Pontypridd.
After spending time with Llanelli and fellow Guinness PRO12 side Scarlets before moving to England, Harris now has a fight for the hooker's jersey alongside Elliot Dee, Rhys Thomas and Rhys Buckley.
"I'm delighted to have joined the Dragons," said Harris. "They are a great team with huge potential as demonstrated during the last two European Rugby Challenge Cup campaigns. Hopefully I can add to what seems to be a competitive environment.
"I am looking forward to coming home to Wales and playing alongside many familiar faces, one being Sam Hobbs who is also a Brecon boy.
"I cannot wait to get stuck into pre-season and work alongside Kingsley and Ceri (Jones, forwards coach), who I believe can add a lot to my game."
Harris, who has also played for his country at under 18 and under-16 level, is head coach Kingsley Jones' sixth addition for the upcoming campaign.
Jones added: "Darran is an exciting prospect with fantastic pace and power.
"Having spent last season in the English Championship with Rotherham his set piece play has developed measurably and he will bring competition for places.
"Darran is a great addition to our squad."
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