While Guardiola did not have the best season with City last term, his side completed an impressive league title win thanks to their rivals Manchester United losing to West Brom at the weekend.
City are a massive 16 points ahead of United, with five games remaining, which saw them mathematically clinch the title.
And Xavi believes the outcome was never in doubt.
"It's a huge achievement for him," said Xavi. "There is so much competition in England. There are so many teams that can win the league," said Xavi to the Daily Mail
"I did an interview a year ago when they were criticising him a lot. And I said then that he just needed time. If they were patient with him then he would end up succeeding.
"Managers get constantly judged and criticised and he is, if not the best, then one of the best two or three in the world, so the pressure is huge. But he has made City champions and he's done it in a spectacular way."