Trevor Mulindwa, 21, was found with six terrorist and propaganda films after being arrested at Heathrow on his way to Mogadishu in September 2014 - including one about a UK jihadi who went to fight in Syria.
He had converted to Islam in August the previous year, and became “particularly interested” in the Al-Shabaab group, an Al Qaeda offshoot responsible for atrocities across east Africa.
Mulindwa had been discharged from hospital as a prisoner on licence just two weeks before he was intercepted at Heathrow.
He was today convicted at Kingston Crown Court under Section 5 of the Terrorism Act of preparing to go to Somalia with the intent of joining Al-Shabaab, a proscribed organisation.
Commander Richard Walton, of the Met’s Counter Terrorism Command appealed to London’s Muslim community to contact Scotland Yard if they become aware of anyone who is planning to travel abroad to fight alongside terror groups.
He said: "Al-Shabaab have been engaged over the past years in a range of terrorist atrocities in Somalia and Kenya and have also in the past planned attacks against the UK.
"We are now faced with the challenge of radicalised British nationals attempting to join many different terrorist groups in a variety of different countries.
“We will continue to do all we can to stop their travel to prevent them becoming trained terrorists and potentially returning back to the UK as a greater threat with the intention of carrying out attacks here.”
Mulindwa, of Mitcham, is due to be sentenced at Kingston Crown Court on Thursday, December 17.