The 22-year-old midfielder agreed to join Boro weeks ago but the move was delayed following his involvement at the Tokyo Olympics for Argentina.
Payero becomes the Teessider’s sixth signing of the summer, following the arrivals of Joe Lumley, Uche Ikpeazu, Sammy Ameobi, Lee Peltier and Matt Crooks.
He has signed a three-year deal.
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Payero was put through his paces on the Rockliffe training pitches by Neil Warnock and Kevin Blackwell and will meet his new team-mates for the first time on Friday.
The central midfielder, who was attracting interest from a host of clubs on the continent, arrives at Boro fresh from the Tokyo Olympics where he featured in his country’s three group matches.
A delighted Warnock said: “Martin will be a great addition to the squad.
“I think he will be an exciting signing, we’re delighted to get everything done, and we’re looking forward to working with him.
“I know Martin is looking forward to it, and he can’t wait to play in front of our fans.”
The player has made 60 domestic appearances in Argentina, for Banfield and Talleres, and he also trained with the national squad.
Boro are also expected to announce the appointment of Kieran Scott as the club’s new head of football.
Scott is set to leave his role as head of recruitment at Norwich, where he has gained a strong reputation and helped the team win two promotions from the Championship.
The appointment is set to see Scott work closely with Boro’s chief executive Neil Bausor and oversee recruitment operations.
“They’ve brought a new sporting director in who is starting shortly so I would imagine things will change in the next 12 months,” added Warnock.
“I’m not going to be working ten years so they have to look forward to the future so that doesn’t bother me.
“They have to think what’s right for the club and then look forward to how they are going to sustain it.
“Everyone is looking for something different and they’ve decided to go down that way.
“We’ll have to see what happens and he’s a good bloke apparently from what I’ve heard.”