The FX series follows the misadventures of four friends working in Irish bar Paddy's Pub in Philadelphia with "bad attitudes, big egos and a penchant for anti-social behaviour".
Charlie Day, Rob McElhenney, Glenn Howerton, Kaitlin Olson and Danny DeVito star in the sitcom, which has been jokingly billed in the past as "Seinfeld on crack".
Netflix members will be able to watch It's Always Sunny streamed over the internet to connected TVs, tablets, game consoles, Blu-ray players, computers and mobile phones. Netflix offers instant and unlimited access for £5.99 a month and is currently offering free month trials.
It's Always Sunny in Philadelphia seasons 1-6 are on Netflix now. Season 7 will be made available on February 13.
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