The 20th world-ranked Klaasen decided to team up with Paes, 41, an eight-times grand slam doubles winner, eight times runner-up and with 54 ATP doubles titles to his credit.
Klaasen, 32, enjoyed what was easily the best year of his tennis career in 2014 in partnership with American Eric Butorac, with whom he reached the final of the Australian Open grand slam event and won five ATP titles.
Paes was troubled by injuries this year, with his long and illustrious career apparently on the decline.
"Cutting ties with Eric (Butorac) was one of the most difficult decisions I have made in my life," said Klaasen in a conference call from Cape Town.
Klaasen had just returned from his honeymoon when he made the announcement.
"It was not only because my career took a dramatic upward turn in partnership with Eric. We enjoyed such a good relationship off the court as well and were really good friends.
"It was difficult confronting him and telling him of my decision. I was not looking for another partner at all." Klaasen said when Paes approached him a couple of months ago to play together in 2015, he was both excited and flattered, but also faced with the realisation that he had a very good thing going with Butorac.
"The invitation from Paes came like a bolt out of the blue. There are not too many other players who would have caused me to make the switch. He was always one of the fittest and fastest players on a doubles court. He is now in pretty good shape," said Klaasen.
"Even though his world ranking has now dropped to 29th, he is quite capable of doing what Roger Federer did this year and bouncing back after many of the pundits had said he was finished in 2013.
Klaasen said the reason for changing his doubles partner was that his ambition remained to win a grand slam title during his career -- and he believed he could achieve this with Paes.
"At the same time, I understand there is a risk involved whenever you try something new and with Butorac we had already cemented a partnership," he said.
Klaasen hopes with Paes he can reach the ATP World Doubles Final, having narrowly failed to make the eight-team event with Butorac this year.
Klaasen and Paes will play together in the Auckland Open in New Zealand early in the New Year and then go onto Melbourne for the Australian Open.
"We might make our debut together in an earlier event as well."