On Thursday morning it was announced that Barrow would be leaving Leicester with immediate effect and would be joining La Rochelle on a deal until the end of the season.
After that, Barrow will become a Saints player, moving to the club in time for the start of the 2018/19 campaign.
The 25-year-old will help to fill a void that is likely to be left by Michael Paterson's departure, with the 32-year-old out of contract at Franklin's Gardens this summer.
Barrow has plenty of pedigree, having enjoyed a two-year stint with Newcastle Falcons after a spell in Yorkshire Carnegie's Academy.
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He moved to Leicester from Newcastle and made more than 50 appearances for the Welford Road club, earning a supporters' player of the year nomination in 2017.
And the former England Under-20s international is delighted to be making the short trip across the east midlands to link up with Saints.
“I’m really relishing a new challenge at Franklin’s Gardens,” Barrow said.
“Chris Boyd’s appointment was key to my decision and it seems to have generated a lot of positive energy at Saints.
"It’s obvious that there’s a huge focus on putting things right for next year and challenging for honours – I can’t wait to play my part.
“I know just how electric the atmosphere is at Franklin’s Gardens and how passionate the supporters are having played against Saints on several occasions – I hope I can do those supporters proud wearing black, green and gold.”
Having captained England’s Under-16 and Under-18 age groups, Barrow made his senior debut for Yorkshire in the 2010/11 European Challenge Cup.
Standing at 6ft 8in, Barrow naturally impressed, joining England’s Under-20s set-up in 2013 and winning the IRB Junior World Championship title with the squad later that year.
That paved the way for a breakthrough move to Newcastle Falcons in the summer of 2013, before he joined Tigers two years later.
And Saints’ interim head coach Alan Dickens believes that Barrow will be another superb addition to Saints’ second-row options for next season.
He said: “Dom offers a lot around the park as well as in the lineout, and we’re delighted to welcome him to Franklin’s Gardens.
“Even though he’s only 25, he’s already proven his huge talent at the highest level on a rugby pitch.
“Dom’s got a lot of rugby in him as well as international aspirations, and we’re really looking forward to seeing what he can add to our game next year.”