"Most of the Sharks have a similar portfolio," O'Leary told CNBC on Wednesday. "It's an amazing index on America's economy because they're almost in every state, in every sector."
O'Leary along with investors Mark Cuban, Robert Herjavec, Barbara Corcoran, Lori Greiner and Daymond John put up their own money on "Shark Tank" to buy stakes in start-ups looking for capital and influential business partners.
"I can report to you, on a private basis, I've never seen a stronger economy in my life," contended the 65-year-old O'Leary. "This is fantastic with what's going on."
Among O'Leary's investments from the show are Wicked Good Cupcakes, Basepaws, a cat DNA testing service, and the fingerprint enabled BenjiLock padlock.
But his biggest success was Plated, the meal kit service that was purchased by grocery giant Albertsons for $300 million in 2017. Plated almost didn't happen for O'Leary. Cuban originally struck a deal with the start-up but it fell apart. O'Leary, later impressed with the company's development, invested.
O'Leary made a fortune selling an education software company that he founded in his basement in 1986 to Mattel for $4.2 billion in 1999. He later started the O'Shares investment firm, which provides exchange-traded funds for long-term wealth management.
Wednesday on "Squawk Box," O'Leary jokingly described himself politically as "a little right-wing of Attila the Hun." However, he's a conservative who tends to side with President Donald Trump on economic and business policy matters.
Under Trump, the economy was on fire in 2018. But this year, it appears to be slowing and perhaps reverting to the slow-but-steady-growth pattern seen by his predecessor, Barack Obama. Next week, the government releases its first look at second-quarter gross domestic product.
Disclosure: CNBC owns the exclusive off-network cable rights to "Shark Tank."