Brittain is the first arrival of the summer and the first new signing under the Dane’s tenure as manager of the club.
Upon confirming the move, the 24-year old took the time to post to social media his message of gratitude towards his former side and its supporters.
The full back has signed a four year deal to keep him at Ewood Park until 2026.
But he wished everyone at Barnsley a fond farewell having spent two years at Oakwell.
“My time at @BarnsleyFC has come to an end,” said Brittain, via Twitter.
“I would like to say thank you to all the fans, staff and my team mates for all welcoming me and giving me their full support over the past two years.
“I wish everyone involved with [the] club all the very best in the future.”
My time at @BarnsleyFC has come to an end. I would like to say thank you to all the fans, staff and my team mates for all welcoming me and giving me their full support over the past two years. I wish everyone involved with club all the very best in the future ❤️ #uuuredssss
— Callum Brittain (@CallumBrittain1) July 21, 2022
Brittain quickly established himself as a key player with the Tykes upon his arrival from MK Dons, playing 76 times in the Championship across two seasons for the club.
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In that time, he helped the team reach the play-offs under Valerien Ismael. But a disappointing follow-up season for the club saw the team relegated in 2021-22.
Blackburn will begin their season on July 30 as they face the visit of QPR.
This will be a very good signing for Blackburn, especially given the loss of Ryan Nyambe to Wigan Athletic.
But it does mean Barnsley have lost one of their most important players, showing a very severe consequence for such a dismal campaign last season.
It will be difficult to find an adequate replacement for the Tykes as they aim to compete for a place back in the second division this year.
Tomasson will be happy to have brought in his first signing of the summer and is likely an indication that further transfer activity will follow suit.