China's Liang led for most of the match, winning the seventh frame on a respotted black to go 5-2 ahead.
Trump hit back, and with the score at 7-6, both players looked nervy and missed shots, but it was the Chinese player who clinched a crucial frame.
Despite missing more chances, Liang held his composure to beat the Englishman and take the £70,000 prize.
Trump had been in good form leading up to Sunday's match, after beating Ronnie O'Sullivan in the final of the European Masters last week.
But Liang became just the fourth player from Asia to win a ranking event, after Ding Junhui of China, Hong Kong's Marco Fu and Thailand's James Wattana.
The 29-year-old world number 20 said he had met former Manchester United manager Sir Alex Ferguson in his hotel before the final, who told him to "concentrate".
However, Liang thanked his "best friend" - five-time world champion Ronnie O'Sullivan - for advising him to learn from last year's UK Championship final, when Liang lost to Australian Neil Robertson.
"I practise with [O'Sullivan] and eat with him every day," said Liang. "I have learned a lot from him over the past two years.
"I knew I needed to be more calm and controlled this time. In the last two frames I concentrated on every shot and made two good breaks.
"Snooker is a very difficult game but if you don't enjoy it you don't play well."
World number three Trump said: "Liang was playing with freedom and his long potting was unbelievable. It's good to have another winner from China."
Liang Wenbo won his first ranking title by beating Judd Trump 9-6 in the English Open final in Manchester.