A slowing economy and more cautious Federal Reserve next year could extend the longest bull run in history, Leuthold Group's Jim Paulsen told CNBC on Thursday.

The strategist is the latest to join a growing chorus, including Art Cashin of UBS and Guggenheim's Scott Minerd, saying the Fed "is done raising rates and maybe will even cut rates" instead of going through with two more hikes in 2019. The central bank last week lowered its rate rise projection for next year from three to two.

"I think we're going to slow below 2 percent over the next four quarters into 2019 and that might just be enough to ... put a pause button on the Fed and bond vigilantes, and I think allow one more run in this bull market," the chief investment strategist at Leuthold Group said on "Squawk Box."

Paulsen said the Fed would likely raise the cost of borrowing money next year if the economy maintained growth of more than 3 percent and record low unemployment below 4 percent.

Last week, Paulsen said that a deeper correction could help markets bounce back from a historic December sell-off. He said that traders were conflicted by an overheating economy and a "stagflation mindset."

Many investors are preparing for a rough 2019, in part on fears that the economy could fall into a recession. The Dow Jones Industrial Average and have slid more than 7 percent and the Nasdaq Composite is down more than 5 percent year to date.

But Paulsen shrugged off any suggestion that a recession would materialize, revealing that he's now as bullish as he was in the latter part of 2017.

"I think we're going to skip a recession at least in the foreseeable future," he said.

Paulsen advises that investors should "get more aggressive again for the first time in a while."

"I don't know where the bottom is here and it's going to be volatile for a little while now, but I think it's time to lean back towards [a] more aggressive stance in your equity portfolio," he said. "I don't know if we'll set new highs than we've already seen, but I think we're going to have a pretty good 2019."