The 50-year-old former Paraguay boss succeeds Tito Vilanova, who stepped down from the role on Friday after one season in charge as he continues his battle with cancer.
Both Martino and Messi are from the Rosario region of Argentina and the four-time Ballon d'Or winner has spoken in glowing terms about his compatriot in the past.
And Martino reckons Messi put in a good word for him with the Barcelona hierarchy.
"I don't know the details of the situation, (but) I have no doubts that Messi spoke with the club directors. I'm sure that Jorge (Messi's father) and Leo have had some weight in this decision," Martino said in a press conference in Rosario this evening.
"They've given their opinion and we've arrived at this end.
"How much weight their opinions held in the decision I don't know but I'm grateful."
He added: "To coach Barca us an extremely important opportunity. I'm very grateful that Barcelona have gone for me and my coaching team."