The 27-year-old flanker has enjoyed an impressive three-year stint with the Titans, making 63 appearances and establishing himself as one of the best performers outside of the top flight.
He will leave Clifton Lane at the end of the season.
"I've loved every minute of my time at Rotherham and learned a lot during my time at Clifton Lane," said Dickinson.
"The supporters have been fantastic and I appreciate all the support they have given me during my time at Rotherham. I am however really looking forward to the challenges that lay ahead and of testing myself with the step up to Premiership rugby."
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