The 31-year-old returns to Sandy Park from Guinness Pro 12 outfit Ulster, where he has featured since 2011 following a two-year stint with Harlequins.
Larne-born Stevenson had previously spent two years at Exeter between 2007 and 2009 and returns with the Aviva Premiership title chasers having suffered injuries in the second-row department to Damian Welch and Mitch Lees.
"Initially when Damo (Welch) went down we thought we would be able to ride through the situation with what we had," Chiefs coach Rob Baxter told the official club website.
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"However, once Mitch got injured we had to re-assess things, not just in terms of getting people to play, but also to ensure we had enough bodies for training.
"Obviously we've looked at the market to see what options are out there and once we knew Lewis was available, we've worked very hard to get him back here to the club.
"Having played here before, Lewis knows the club and we know him.
"We're very aware of the qualities he can bring to the squad and what kind of character he is, so he ticks a lot of boxes for us."
Stevenson made 62 appearances for Exeter in his first spell at the Devon club and said they had made huge strides both on and off the pitch since.
"Since I've left the club have established themselves as a real force within the Premiership and each year they seem to go from strength to strength," Stevenson said.
"For anyone on the outside, they are a real example of how to get into the Premiership and stay there."
Stevenson will join up with the squad in time for second-placed Chiefs' Premiership trip to Worcester Warriors on Saturday.
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