Cox joined from English Premiership club Sale Sharks on a one-year deal in the summer and has featured in seven of 11 games so far this season, taking to the field at lock and back-row.
Now, with the season nearing its half-way point, head coach Michael Bradley has moved to retain the Manchester-born enforcer for another two seasons.
He said: "Sean [Cox] has been a very good professional in terms of his attitude, his training and work rate.
"He's a good organiser, leader and communicator on the pitch and he's quite a physical player too so all of these attributes led us to the conclusion that he's a good fit for Edinburgh Rugby and we're delighted that he's signed for another two years.
"He's very important to the future of the club."
Cox is the latest quality forward to commit his future to Murrayfield, following on from the extension of back-five trio Steven Turnbull, Stuart McInally and David Denton.
Reflecting on what lies ahead at Edinburgh Rugby, Cox added: "It's a very exciting place to be at the moment. There are a lot of good ideas and talented young players who have also committed to the club.
"There's a clear statement of intent being made by signing players early. It's really exciting I'm delighted to be part of it but this is just the start. It's down to the players to deliver their part of the club's vision on the field."
Michael Bradley added: "It's fantastic news for us as a club that these players want to stay with Edinburgh Rugby. They see a positive future for themselves and that they can reach their ambitions playing at this club."
Sean Cox (26), lock/back-row, 113 kg, 6ft 5in, 16/01/1985
Cox began his rugby career in school-boy rugby, favouring the round-ball game in his earlier years before turning to rugby during his time at school. At the age of 18 he was chosen for the England schools set-up which led on to his selection for England under-18, U19 and U21, while becoming affiliated full-time with Sale Sharks, turning professional aged 19. He spent six seasons in the first team at Sale Sharks before signing for Edinburgh Rugby in the summer of 2011.
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