The groups, which are run by representatives of the players and tournaments, have hired consultancy McKinsey & Company, one of the people said. A second person said the appointment happened earlier this year.
A deal could value the emerging entity at around 3 billion pounds ($3.84 billion), two of the people said.
The ATP and WTA said in a statement that they are "exploring discussions that would enable us to leverage assets across both Tours via the creation of a new joint commercial entity, delivering more value to players, tournaments, and fans, while remaining as separate Tours".
The talks are still in the preliminary stages, they added.
The move would bring all the commercial ventures into one entity, with the aim of completing a merger in 2025, the first person added, speaking on condition of anonymity because the matter is private.
A deal would allow the two groups to reduce duplication in their organisations and to more effectively market themselves to broadcasters and sponsors, the person added.
It would build on a deal done last year between the WTA and private equity fund CVC, which gave CVC 20% of a new company overseeing the broadcasting and marketing operations of the women's tennis association called WTA Ventures, they said.
CVC and McKinsey both declined to comment.
More financial investment could be required as part of the merger, two of the people said. The sport has also drawn interest from Saudi Arabia's Public Investment Fund (PIF), which last month signed a multi-year strategic partnership with the ATP.
PIF is also interested in investing in a tournament, a person with knowledge of the plan said, possibly an addition to the existing nine ATP Masters 1000 tournaments that feature the top-ranked players in the tour.
The ATP declined to comment further, but ATP Chairman Andrea Gaudenzi said in January that he had held talks with PIF about possible co-investments in the tour's infrastructure, technology and events, according to Sportcal.
The WTA said it is "engaging actively with the other governing bodies of professional tennis, (and) existing and potential commercial partners, to explore whether we can bring greater alignment across the sport, while reducing the fragmentation that exists at present".
It said there was no consensus over any preferred outcome.
Media speculation that the season-ending WTA Finals could be shifted to Saudi Arabia has intensified in recent months, and it is widely expected to be held there despite notable opposition from Grand Slam champions such as Martina Navratilova and Chris Evert.
The WTA said it was currently working through a process to select a host venue for the WTA Final. "There has been no final decision at this time," it said.
A merger of the ATP and WTA has been discussed for years, and has had the backing of tennis greats such as Billie Jean King and Roger Federer.
WTA chief Steve Simon told the New York Times in 2020 that they compete against themselves and other leagues for fans, sponsorships and broadcast.
Tennis fans need different pay-TV platforms to watch matches, and a merger could simplify television contracts and sponsorship deals.
