McCusker continues his duties as captain after a successful past year that saw him lead the Scarlets to a RaboDirect PRO12 semi-final in May 2013.
The honour of the West Wales armband will be shared with British & Irish Lions centre Davies, who has previously captained the regional side in McCusker's absence.
With close to 200 Scarlets appearances between them, the two captains have grown up in Scarlets rugby alongside each other with Davies now entering his eighth senior season with the club and McCusker his seventh.
The role will see the duo alternate as skipper during different blocks of rugby over the season, according to specific game day requirements and preparations in any one training week.
"We are delighted to have Rob and Jon leading our side this season," said Scarlets head coach Simon Easterby.
"They are committed and ambitious professionals with an exemplary work ethic and the ability and experience to take our team forward.
"They will set the benchmark for a number of our up-and-coming young players who look to senior players for vision and leadership during the more intense times in our season.
"Both expect very high standards and lead from the front in terms of their own performances. This will undoubtedly have a positive impact on the whole squad. They have the full respect and backing of all our players and management team and I know they will do an excellent job.
"Equally important to our region and our supporters is that both of them embody what being a true Scarlet is all about having grown up playing rugby in our region."
Easterby explained the decision to appoint co-captains this season came from a review of last season and the work that has been done over pre-season preparations this summer.
"We will also have a leadership group working below the co-captains which allows us to continue our theme from last season's review," he added.
"With a squad with an average age of 24 compared to many of the Heineken Cup teams averaging at 29 plus, we need leaders in our group to set the standards and progression of Scarlets rugby this season."
With both players boasting international experience and Davies returning to Parc y Scarlets after impressing hugely on the British & Irish Lions tour to Australia, the Scarlets certainly won't lack for leadership.
Easterby said: "Jon is an established world-class centre for Scarlets, Wales and now the British & Irish Lions. He has the full respect of his Scarlets colleagues and takes great pride in having his rugby roots in West Wales.
"I've been really impressed with how Jon has grown in stature as one of our senior players and he thoroughly deserves this opportunity to lead his region."
On McCusker, he added: "Rob has earned the respect and full support of his Scarlets team mates over the past season and has been a natural leader for us.
"He has worked incredibly hard for the Scarlets region and will ensure continuity in leading our progression this season."