The defender is moving north for an undisclosed fee and has signed an initial three-year deal.
Albion boss Graham Potter said: “Matt wants to play and we can’t give him that guarantee. The move to Middlesbrough gives him that opportunity.
“He was an excellent professional during his time with us and was a pleasure to work with. We wish him all the best for the future and the coming season.”
Clarke joined Albion from Portsmouth three years ago but has never played in the Premier League.
Loaning first to Derby and then West Brom in the Championship and making 110 appearances in total over the three years, his performances have caught the eye of Boro boss Chris Wilder though.
https://www.theargus.co.uk/sport/20757580.middlesbrough-sign-brighton-defender-matt-clarke/?ref=rss Middlesbrough sign Brighton defender Matt Clarke