The Utah Republican -- who promised in 2012
that his current term would be his last -- said he has changed his mind at this time, partially because he's been getting encouragement from President Donald Trump and top Republicans to run again.
"I'm planning on (running) right now," Hatch told CNN Thursday. "That's what my current plans are."
Hatch, who will turn 83 later this month and has served in the upper chamber since 1977, could still change his mind again and decide to retire.
Asked by reporters later after CNN reported on his remarks, Hatch said: "Well let's put it this way: it's just too early to make a decision. My intention is to continue to serve Utah."
But his Thursday comments are the firmest signal yet from the most senior Republican senator, who is third in the line of succession to the President as the Senate's president pro tempore.
The decision comes as Senate Majority Leader Mitch McConnell and Trump have both tried to persuade the powerful chairman of the Senate Finance Committee to run again.
"His pitch is he needs me," Hatch said of Trump. "Things are going to be just fine."
Hatch's decision comes as Trump has chosen Jon Huntsman
, the former Utah governor, to be his nominee for ambassador to Russia. Some had speculated that Huntsman would have mounted a primary challenge to Hatch in 2018.
But Hatch said he spent an hour Wednesday with his "longtime friend" Huntsman and said he believed that the ex-governor was not going to challenge him.
Hatch said he had no role in getting Huntsman the post.
"I don't think he would have ever run against me," Hatch said. "He didn't really want to run for Senate."
Asked if he was preparing for a tough 2018 reelection battle, Hatch said: "Anyone who wants to take me on knows it's going to be a real ordeal."
This story has been updated to reflect breaking news.