Manager Phil Parkinson moved back into the market after January signing Bailey Wright was ruled out for a period of eight to twelve weeks with an ankle ligament injury.
29-year-old Smith made over 200 appearances in the Championship for Ipswich over a ten-year period, before spending two seasons with MLS side Colorado Rapids.
Crucially, Parkinson believes he is capable of playing acorss the back three and so bolsters his options ahead of a crucial few months.
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Smith has been without a club since late November but has been training at his former club in Suffolk to keep up his match fitness.
Smith was put through a series of physical assessments on Wearside, with Parkinson clear that he would only make a further addition if they would be available for selection in the near future.
While Smith is clearly a touch short of match fitness, the Black Cats are confident that he is capable of providing experienced cover in the weeks and months ahead.
The defender trained with his new team-mates on Friday.
Alim Ozturk is set to return to the side against Bristol Rovers on Saturday, while Conor McLaughlin is also capable of deputising on the right of a back three.
Joel Lynch returned to training this week, but his recovery from a rib problem will continue to be monitored closely.
“Lynchy is back in training today, so I'm pleased with that,” Parkinson said on Thursday.
“In terms of the concussion he was fine but the bruising on the ribs was a problem.
“But in the last two or three days he's made great strides. That's good news for us and brings him back into the picture, if not for the weekend then certainly for Tuesday.”
Wright is set to stay on Wearside for the rest of the season to continue his rehab, with a return to action not yet completely ruled out
Parkinson confirmed on Thursday that he had moved to the area after joining on loan, and could yet sign a permanent deal this summer.