The Ireland out-half will join Racing Metro at the end of the season, but his long-time friend and team-mate revealed Sexton was originally very upset at the prospect of having to join a team other than his beloved Leinster.
"There's no point in lying about the whole thing. Jonny will tell you that he wanted to stay and was upset," revealed Kearney.
"He wanted to agree a new contract and play in Ireland but, whatever way negotiations went, unfortunately, you don't always get what you want."
Kearney and Sexton have been team-mates since they were 14 years of age playing schoolboys rugby with Leinster. When you have that length of association and relationship with your club, there is, Kearney insisted, a longing desire to fulfil all your playing ambitions with that team.
"When you grow up in the province and you have come up through the system, there is a real love for that team," he said. "You want to play there, especially when the team is competitive and you are challenging for trophies every year.
"In that situation, which we have at Leinster, there is no need to leave."
Sexton, of course, will have a reputed €750,000 annual salary to dilute his disappointment at leaving Leinster and Ireland. He is also looking forward to starting a new life in Paris.
"Jonny's now at the stage where he's excited about the whole thing. He's getting married to a lovely girl in the summer and they will jump into their new life head first, like he has always done through his life.
"This is a new chapter for them and one I am sure they will enjoy thoroughly," said Kearney (below).
Sexton is the first high-profile first-team Ireland player to accept a contract outside the Irish system since Keith Wood decamped to the English Premiership. Sexton's move will be one that other Irish players follow closely.
"It can go either way in that it could go all wrong. But if it works well for him – as I expect it to – he is enjoying life, playing good rugby, winning trophies and earning more money, it could open up a whole new ball park for Irish players," said Kearney.
"There's a certain amount of bravery on Jonny's part and guys will certainly be watching how it goes."
Sexton's decision to reject the IRFU's offer has the potential, as Kearney indicated, to pave the way for more Irish players to seek better paydays elsewhere. This should be causing sleepless nights in the corridors of the IRFU.
Kearney, for example, has yet to agree a new contract with the union, and he is not alone. The IRFU's archaic policy of waiting until, usually, the November internationals before entering negotiations is now looking a very dangerous one.
It is an ongoing cause of frustration for the players.
"I was always very keen to get it (contract) sorted before the Six Nations, which obviously isn't the case," said Kearney.
"It is a difficult place to be in, when you are trying to determine your future and play the biggest competition of the year as well. It is probably not ideal that the talks always fall around this time.
"Certainly, I've just parked that a little bit and my sole focus is on performance – it has to be a little bit because if you get caught in both, both are going to suffer.
"You have to make a decision, choose one, give it all your attention and hopefully the periphery stuff follows."
Kearney is only recently returned from injury and said he hadn't received any overseas offers. That, however, could change after the Six Nations.
The full-back was outstanding on the last Lions tour and if he hits that peak again, Ireland will surely do well in the Six Nations and his services will be in high demand.
"I'm sure if I went looking, there would be options there. I'm only two-and-a-half games back from injury so I'm in a little different a situation, but you are always in the shop window a little in a big tournament like the Six Nations," he said.
"You do think about moving away, and the last time there were options. But when you are with a club you've grown up with, enjoying playing with your colleagues and your friends and you are winning trophies in Europe, it is very difficult to justify why you would want to leave.
"The thought has always been there, but I've never really had any reason for wanting to leave."