Nick Pope, who formerly investigated UFO reports for the Ministry of Defence (MoD), thinks NASA will find aliens in the next five to 10 years.
The UFO expert told Express.co.uk NASA will most likely unearth evidence of alien microbes or plants somewhere within the solar system.
But the discovery of intelligent extraterrestrial life could be the real crowning glory for the US space agency.
The news comes after a team of 17 scientists urged NASA to search for alien biosignatures on all of its future space missions.
A similar report published earlier this year encouraged NASA to scan the universe for signs of artificially created alien technosignatures.
However, Mr Pope argued it is only a matter of time before NASA’s efforts yield positive results.
He said: “Finding microbial or simple plant or animal life beyond Earth would be amazing, but the real prize would be discovering there are other civilisations out there.
“Thus, technosignatures are a bigger and better goal than biosignatures and I’m pleased to see NASA putting more resources into this.
“I firmly believe that it’s only a matter of time before we find alien life.
“It will happen in the lifetimes of most people reading this article, and I wouldn’t be surprised if it happened in the next five to ten years.”
The best chance of success comes from big-budget research projects like the proposed multi radio telescope Square Kilometre Array (SKA) in Australia and Africa.
The ambitious international project would scan the cosmos with thousands of individual satellite dishes and up to a million low-frequency antennas.
But Mr Pope argued there is still a need to “this outside of the box” and it is a good thing NASA’s Technosignatures Workshop is developing new technologies to find alien life.
He said: “My hope is that artificial intelligence plays a part, because ‘robots find aliens’ would be the best headline ever.
“In any search, it’s good to cover all the bases, and a multi-pronged search probably stands a better chance of success than putting all our eggs in one basket.
“Thus, while I think focusing on technosignatures is sensible, we shouldn’t stop looking for biosignatures, and neither should we ignore UFO data.
“It would be a sad irony if, after all the time and money spent looking for alien life, we find it not ‘out there’, but ‘down here’.”
At the same time, the UFO expert said all of NASA’s efforts will be in vain if the space agency does not prepare beforehand for the potential hazards associated with the discovery of alien life.
These hazards include alien viruses and harmful bacteria but also the possibility of hostile civilisations paying a visit to our home world.
Mr Pope said failing to prepare for the first contact with extraterrestrials is a big mistake and something has to be done about it.
Which is why he shared with Express.co.uk a five-page-long contingency plan, outlining a potential contingency plan that could be enacted once NASA finds life in space.
Mr Pope said: “I’ve recently drafted a contingency plan for the detection or discovery of extraterrestrial life, which I hope governments and the scientific community will consider.”