Daniels won promotion with Brentford last term, playing ten times in all competitions.
But the 33-year-old wants regular football and will be hoping to make an impact at Boro in the coming season.
Boro coach Neil Warnock said, per the club website: "I've watched Luke for a few years now and I'm delighted to have him on board.
"I've always found him very consistent in what he does.
"He's a good keeper, a good lad, and he'll be a great addition to our squad."
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