Delivery driver Junead Khan, 25, used his job with a pharmaceutical firm as cover to scout United States Air Force (Usaf) bases in East Anglia, his trial heard.
Detectives later found he had been exchanging chilling online messages with an Islamic State (IS) fighter in Syria calling himself Abu Hussain at the same time, including describing attacking military personnel after faking a road accident, The Press Association reported.
Prosecutors claimed Hussain was in fact British-born fanatic Junaid Hussain, who was killed in a US drone strike in the IS stronghold of Raqqa just weeks after his link with the planned UK attack was discovered.
After Khan was arrested in July, police found pictures on his phone of him posing in his bedroom with an Islamic State-style black flag which they later found in the attic. His computer was also found to contain an al Qaida bomb manual and Amazon searches for a large combat knife.
Khan was found guilty of preparing for an act of terrorism in the UK between May and July 2015 after a trial at Kingston Crown Court in London.
He was also convicted alongside his uncle, Shazib Khan, 23, of preparing to go to Syria to join IS. Some of the evidence used to convict the pair cannot be revealed for legal reasons.
Both men had denied engaging in conduct in preparation of terrorist acts between August 1 2014 and July 15 2015.
Neither showed any emotion as the jury returned its verdicts after deliberating for almost 24 hours at the end of a six-and-a-half-week trial.
Judge Mr Justice Edis remanded the men in custody ahead of sentencing on May 13.
Junead Khan was found guilty unanimously of planning a UK terror attack but by a 10-2 majority on the second charge of planning to travel to Syria.
Shazib Khan was found guilty by unanimous verdict.
Junead Khan's work as an agency driver for pharmaceutical firm Alliance Healthcare legitimately took him to East Anglia in May and June 2015, the court heard.
During these trips he drove close to bases operated by Usaf - RAF Mildenhall and RAF Lakenheath in Suffolk, RAF Feltwell in Norfolk, and RAF Alconbury and RAF Molesworth in Cambridgeshire.
He was arrested on July 14 at Alliance's depot in Letchworth, Herts.
The trial heard that in one of their July 5 conversations on the encrypted SureSpot app, Junead Khan talked to Hussain about faking a road accident before getting out to attack people directly, and carrying a bomb.
Hussain said: "I can get you addresses but of British soldiers" to which Khan replied "that could also be possible".
Hussain added: "Most soldiers live in bases which are protected. I suppose on the road is the best idea. Or if you want akhi I can tell u how to make a bomb."
Khan then told Hussain: "When I saw these us (sic) soldiers on road it looked simple but I had nothing on me or wouldve (sic) got into an accident with them and made them get out the car."
Hussain replied: "That's what the brother done with Lee Rigby."
He went on to say he would send Junead Khan a manual for making a "pressure cooker bomb", adding: "It's best to have at least pipe bombs or pressure cooker bomb in a backpack in case something happens - so you can do isthishadi bomb in case they try arrest you."
Junaid Hussain was married to Kent woman Sally-Anne Jones, a British former member of an all-girl punk rock group turned jihadi bride.
He was one of the British IS killers whose personal details were in documents released this month after reportedly being stolen by disillusioned IS soldier.
Jurors were not told this or of his senior position in IS, simply being told he was in Syria and had later been killed in an American drone strike.
The prosecution had alleged that Junead Khan planned to travel to Syria with his relative but altered his plan to focus on an attack in the UK, either on British or US service personnel.
Giving evidence in court he said while he supported the establishment of an Islamic State, he did not wish to become a fighter himself.
Shazib Khan admitted exchanging messages with friends saying they had a "role to play" and that he wanted to help "by any means", but insisted he meant through providing money and food, not violence.