Boro host West Bromwich Albion in their season opener and Chris Wilder has bolstered his defensive ranks with the addition of former Huddersfield Town captain Smith.
Smith, 30, has been involved with Boro throughout pre-season having been handed his first start for the club against Bishop Auckland last month.
He spent a large part of his early career progressing through the youth ranks at Manchester City before moving to the Terriers in 2012.
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Smith enjoyed over six years at the John Smith’s Stadium, where he also helped guide the club to the Premier League in 2017 after featuring in the play-off final penalty shootout win over Reading.
The Warrington-born defender, who can operate at both right-back or centre-back, joined Stoke City in 2019 and made over 100 appearances for the Potters before his contract expired this summer.
And Wilder has moved to add the experienced defender to his squad ahead of the new season with Smith admitting it’s nice to put the uncertainty of his future to rest.
“It’s been a tough pre-season in terms of the training and the uncertainty,” Smith told the club website.
“I wasn’t sure where I was going to be, or what I was going to do, but one thing I did know was that if Middlesbrough came calling it would be a straightforward answer for me.
“I’ve known the manager for a long time. I know what he’s about and I know how he likes to do things, but ultimately I think he wanted me to come in here to see whether I could fit into the group.
“For me to have been here for the couple of weeks that I have been, it just seems to have worked so I’m over the moon it’s now been put to bed.
“It was always my ambition to get it done as soon as possible.
“It’s taken a couple of weeks longer than I would have liked but I understand this is football and this is what happens but it’s brilliant to get it done, the first game of the season is on Saturday and it’s all systems go now.”
Meanwhile, Boro have also confirmed the exit of defender Hayden Coulson who has agreed to join Aberdeen on a season-long loan.
It will be the fifth loan spell for the Boro academy graduate who has also spent time with St. Mirren, Cambridge United, Ipswich Town, and Peterborough United in recent years.
Coulson has made 49 appearances for Boro since progressing through the academy ranks.
“I want regular football, I haven’t had enough of that in the last couple of years, so now I’m ready to crack on and try to get a place in the team,” said Coulson.
“I had an injury last season when I went on loan at Ipswich and that meant I didn’t get many games there, so I need to prove myself again, that I can play at a good standard and play consistently well and I’m looking forward to the challenge.”