A former Benfica defender Katsouranis very recently led the Greek football team in their campaign at the 2014 FIFA World Cup in Brazil in the absence of regular skipper Giorgos Karagounis.
Kostas becomes the first player and captain of this year's FIFA World Cup to feature in the ISL.
The defensive midfielder will join the likes of former Juventus star David Trezeguet at FC Pune City before they begin their ISL campaign against Delhi Dynamos in New Delhi on October 13.
With him joining the ranks, FC Pune City now becomes a team to watch out for in the inaugural season of ISL.
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Katsourinis made his international debut for Greece in 2003 against Sweden and scored his first goal against Kazakhstan in the 2006 FIFA World Cup qualifier.
Katsouranis was instrumental in Greece's 2004 UEFA Euro win.
"I am happy to represent FC Pune City. This is a new experience and I look forward to add value to the team's targets," Katsouranis said.
"The temperature may be hot and humid in India but I am ready. And anyway football is played from the heart," he said.
Katsouranis is known to be very strong in the air. His natural attacking instinct makes him a valuable footballer as he has the ability to also ghost into the box consistently despite playing in a deep-lying role.
Speaking on Kostas' arrival, Gaurav Modwel, CEO, FC Pune City said, "We would like to extend our heartiest welcome to Kostas. Apart from being a great player, he is an amazing human being - his passion for football, down to earth personality and desire to learn and share sets him apart. His vast experience as a midfielder shall bring great balance to the FC Pune City team.