Neil Taylor has signed a contract extension with the club.
The 32-year-old left-back, who won over 40 caps for Wales, initially joined the club in November when he signed a short-term deal up to mid-January.
Taylor, who left Aston Villa at the end of last season after clocking up over a century of appearances for the club, has made two appearances for the club so far, impressing in the home wins against Bournemouth and Nottingham Forest.
Neil has a wealth of experience, he spent six seasons with Swansea in the Premier League before becoming a promotion winner with Villa, and Boro boss Chris Wilder was delighted to secure his services until the end of the season.
“I’m really pleased we’ve been able to do this,” said Wilder. “Tayls is a great lad, and he has been outstanding. I knew what Neil was about, known what his career was all about, his personality was all about.
“To come into the game against Bournemouth having not played any football or senior football and play in the manner that he did and take that on. Neil Taylor has been outstanding off the pitch as well as on it.
“When (Marc) Bola was playing, Neil was there backing it up. Encouraging in the changing room, a proper team player, waiting for his opportunity.”