A relative unknown until barely a week ago, the Argentinian's biggest role before getting the call from Barca was coaching the Paraguay national team, who he took to the quarter-finals of the 2010 World Cup and the final of the Copa America a year later.
In an interview with Argentinian TV station TN, Martino explained that the president of Paraguay, Horacio Cartes, first introduced him to Barca club president Sandro Rosell several years ago, when the Catalan was a marketing executive for Nike and Cartes ran Paraguay side Libertad.
He said: "It all came about via Horacio Cartes. I met the president of Barcelona [Rosell] at a dinner at Cartes' house. Then, when the Barcelona job became vacant, Rosell didn't know how to contact me so he called Cartes, and that's how it all began.
"Until I'd spoken to Rosell, I had no idea what was going on. He told me he wanted to put me in contact with Andoni Zubizarreta [Barcelona's sporting director] and a few days later we started to talk. I didn't even mention it to my wife."
The Argentinian also said he never thought he would be considered for the Barca job, and thought his best chance at coaching Lionel Messi was in the distant future, if the four-time Ballon d'Or winner returned to his boyhood club Newell's Old Boys, which Martino coached until last month.
"It's all very exciting, but I'm enjoying it," said Martino, who was presented at the Nou Camp on Friday and who last night watched his new side hammer Norwegian team Valerenga 7-0.
"This is an amazing job which brings up many sensations, but one that also carries a great responsibility. This exceeds anything I've done before. Going straight from Argentina to Barcelona is crazy, it would have been more normal to start a career here in Spain first.
"Messi continues to surprise everyone with every game and I'm no different. I believed that he wanted to return to Rosario one day and that at some point he'd return to Newell's, and I thought that's when I'd be his coach. I never imagined I'd coach Messi at Barcelona."
Messi is just one of many big talents and personalities that Martino will have to get used to managing, but he insists he is undaunted by the task.
"I believe that the best way to deal with it is to accept that Barcelona is full of stars and work with them naturally, speaking with them face to face and with respect," he said.
"I think that's the way to move the club forward."