Named Snoopy after the cartoon dog, the four-meter wide module was believed to have been lost forever after the 1969 mission, Sky News reported.
It was used as a test run for the Apollo 11 lunar landing, which took place two months after Apollo 10, in July 1969.
Two of the three astronauts transferred into it, reaching an altitude of 50,000ft above the surface of the Moon, before going back to the command module.
After demonstrating the docking maneuver, Snoopy was shot off into 900 million kilometers of space.
Nick Howes, a fellow at the Royal Astronomical Society, said he is "98 percent convinced" he and his team have found it.
But until someone goes and retrieves it "we can't be 100 percent sure".
Howes began searching for the module back in 2011 and calculated that the odds of locating it were 235 million to one.
He and a team of astronomers analyzed terabytes of radar data and last year discovered what they believe is Snoopy.
"Until someone gets really close to it and gets a detailed radar profile, we can't be sure," Howes said.
"We've got to wait quite a few years for it to come back but once it does come back the idea is that we are going to get a really detailed picture of it.
"It would be a really fantastic achievement for science.
"People say 'what's the point?' From a space archaeology point of view, it's interesting.
"It's the only one that's up there that has flown, that is left. The Apollo program was the greatest technical achievement in human history.
"Anyone of a certain age will know exactly what they were doing on July 20 1969. It's the Kennedy moment.
"As a piece of history, a moment in history, this is a unique artefact."
Speaking at the Cheltenham Science Festival, Howes said someone like SpaceX founder Elon Musk would be the ideal candidate to bring Snoopy back.
He said, "I would love to get Elon Musk and his wonderful spacecraft up and grab it and bring it down.
"As Apollo 10 crew member Eugene Cernan said to me, 'Son, if you find that and bring it down, imagine the queues at the Smithsonian?'."