The 35-year-old left-hander is a prolific T20 scorer, sitting 12th in the format's all-time list with more than 9,000 runs in the format.
He is heading to familiar surroundings, having helped Trent Rockets win last season's Hundred.
"Trent Bridge is a great place to call home," said Munro.
"I've witnessed first-hand how much the crowd get behind the team with the Rockets last summer and when I've been fortunate, or unfortunate, to come up against the Outlaws at home.
"I'm joining a team which plays an aggressive brand of cricket which suits my style and how I like to go about scoring runs. I want to come in and add my experience to what is already a well-oiled machine."
Head coach Peter Moores suggested Munro would help fill the gap left by Australian Dan Christian, who recently announced his retirement, and the likely absence of Ben Duckett on international duty.
"We've spoken a lot about Dan and what he brought to us; experience, quality and a positive and dynamic style of play. I see Colin in the same bracket," said Moores.
"We're conscious of the fact that Ben has done really well for England and there's more than a fair chance that we'll miss him for parts of the summer. That's one of the reasons we wanted to bring Colin in, to make sure we have that wealth of experience to call upon."