The club announced that Kane had signed a deal which takes him through to May 2020.
The 22-year-old has scored 12 goals in 86 appearances for Saints.
Meanwhile, manager Tommy Wright will not allow speculation linking him with the vacant Hearts job to deflect from his team’s Ladbrokes Premiership opener at Kilmarnock on Saturday.
“I’ve no thoughts on it,” Wright said. “I’m preparing for this season with St Johnstone. I’m under contract with St Johnstone.
“I think it’s a measure of how well I have done that I get linked with these jobs but I’m fully focused on Kilmarnock and then Partick Thistle and then Motherwell. I can’t do anything about speculation but my focus is totally on St Johnstone.”
When asked whether he was flattered by the links, Wright said: “We’re in a game where it’s results-based and performance-related and, as long as my chairman is happy, I’m happy. He seems happy enough with me at the minute and that’s all the praise I need.”