The 28-year-old has been a regular for the Pirates in the Championship over the past three seasons and a prolific points scorer.
Joining the Pirates from Nuneaton ahead of 2009/10, the England Counties cap has totalled 249, 413 and 367 points in his three terms at the Mennaye.
However, he is not just a goal kicker. A dangerous counter attacker in particular, he has also scored 26 tries over the same period.
2011/12 saw him named in the Championship Dream Team as he passed 1,000 points in total for the Pirates and chalked up a century of first team appearances.
With Olly Morgan still working his way back to fitness after knee surgery, Martyn Thomas is the only specialist full-back in the squad, so Gloucester director of rugby Nigel Davies is happy to have more options at his disposal.
"Ideally, I like to have three players competing for every position in the side. Olly's doing well with his rehab but we don't want to rush him. If Martyn were to pick up a knock, we'd be short of numbers," he said.
"So, Rob is a perfect addition to the squad. He's been a stand out performer at Championship level for several seasons and brings something different to the table in that he's a quality goal kicker as well.
"We feel that he's ready to make the step up and are delighted that he'll do so in the Cherry and White of Gloucester."
Cook is also delighted to be making the move up to the top flight.
"It's a great opportunity for me and I'm genuinely excited at the prospect as playing in the Aviva Premiership has always been a goal of mine," he said.
"Leaving the Pirates wasn't an easy decision to make as I've spent three great seasons there and made friends for life. They've been great about it all and their result will be the first one I look out for each weekend.
"Once I'd spoken to Nigel, however, and listened to his vision for Gloucester, I knew immediately that it was something I wanted to be part of.
"Gloucester have got a great young squad and I'm just looking forward now to getting down to some hard work with my new team mates in training and making sure I'm ready to go when called upon."
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