It was one of 28 bills the Republican signed Tuesday, his office said in a news release.
House Bill 640 was passed by the Senate in a bipartisan 17-6 vote in May; it sailed through the House, 318-36, on March 8.
At the time, Sununu said he would sign the measure into law, calling it "common sense marijuana reform."
Sen. Jeb Bradley, R-Wolfeboro, worked with stakeholders to engineer a compromise which he fought to protect against amendments proposed by decriminalization opponent Sen. Bill Gannon, R-Sandown.
"The reason I am supporting this bill is personal," Bradley said in May. "A lot of us have kids. I do. Every parent knows kids are what we used to be when we were kids. They try things. I don't want my kids facing one strike and you are out, because I've been there."
Opponents of the bill said it would send the wrong message to youth, especially with the state deep in a drug addiction crisis.
(c)2017 The New Hampshire Union Leader (Manchester, N.H.)