The Colombian looked destined to join Juventus a couple of months ago but has now pledged his future to the Nerazzurri.
The Colombian looked certain to leave San Siro in the winter transfer window and had all but agreed to be part of a swap deal with Bianconeri forward Mirko Vucinic.
However, Nerazzurri president Erick Thohir pulled the plug after fan outcry and his long-term commitment to Inter has now been sealed with a one-year contract extension that could see him stay in Milan for at least another three years.
"Two years have passed since I arrived and it has always been a positive experience, and with every day that has gone by I have learnt a little more. Today I can say that for the next three years I will use those experiences and the positive things I have picked up and make the most of them.
"This is a good moment to say thank you to the president, the coach, the staff, but above all my teammates and the fans because the faith they have placed in me has been so important. Let’s hope I can score to celebrate my new contract, both to help the club to win and to celebrate this special moment."
Guarin, 25, has made 29 appearances for Inter this season, scoring three goals and bagging 12 assists.