The North Walian flanker succeeds Wales hooker Matthew Rees, who stands down after two seasons as skipper.
The appointment of McCusker as captain and that of Simon Easterby as head coach marks the beginning of a new era at Parc y Scarlets.
And McCusker, who continues to recover from double shoulder surgery, hopes to live up to the reputation of the Scarlets captains that have gone before him.
“It’s a big honour and privilege to be asked and I was delighted to be picked as captain after six seasons in the Scarlets shirt,” said the 26-year-old.
“I’ve been fortunate to play under some good guys like Smiler (Matthew Rees) and Easters (Simon Easterby). I have had enjoyed a long lesson from the good captains before me and hopefully I can add myself to that list.
“This region has supported me well as a player coming through and backed my progression. I will give it everything I can to help lead our team and work hard to see us achieve our potential.
“We’ve got plenty of spirit in this squad and it’s an exciting time ahead.
McCusker has skippered the Scarlets in one-off matches in the past and Easterby, who also led the region from the back-row, reckons he is made for the job.
“Having played alongside Rob and then also coached him as a player, I have seen him develop and mature as a player a great deal over the past six years,” said the former Ireland flanker.
“He has earned his stripes, working extremely hard to get his opportunity with the Scarlets — and once he did he hasn’t looked back.
“He has the respect of his peers and coaching group, which is vital. He will lead from the front and by example and I know he will set the highest of standards along the way.”
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