Lee, 49, is accused of embezzlement, perjury and concealment of assets overseas.
Prosecutors allege that Lee was the ultimate beneficiary of a range of crimes that involved four other Samsung executives, including Choi Gee-sung, the former head of its corporate strategy office, who faces 10 years in prison.
Lee, the de facto leader of one of Asia's largest conglomerates, has been in detention since February, on trial for charges ranging from embezzlement to perjury, in a scandal that led to the ouster of former president Park Geun-hye.More news: Manchester United move for Barcelona utility man but face competition from Chelsea
The undertrials had continued false statement and excuse during the past court hearings that lasted for over five months, according to the special prosecutors.
"I have never asked the president for a favor for my private interest or for my own personal gain", he said, fighting back tears.
Special prosecutor Park Young-soo's independent counsel team, formed specially to investigate a massive corruption scandal that led to the country's first ever impeached president, demanded the jail sentence at Lee's final trial held at the Seoul Central District Court.More news: Serena Williams has 50s themed baby shower
In 2015 the group pushed through a merger between two of its units, giving the heir fresh shares in Samsung C&T Corp., a major shareholder in Samsung Electronics.
During Lee's absence, Samsung has released the Galaxy S8 smartphone to rebound from its Note 7 recall previous year and posted a record profit on the back of its semiconductor sales. Prosecutors allege the money was paid to a company in Germany to bankroll equestrian training for the daughter of a friend of then-President Park Geun-hye.
The defence reiterated his denial of wrongdoing, questioning whether the prosecution was relying on public sentiment to secure a prison term for Lee, 49, whose father, the group patriarch Lee Kun-hee, was hospitalised in 2014.More news: Manchester United to pip rivals City to Premier League title - Robbie Savage
He also claimed to have had no role in wider decision-making at Samsung and "mostly listened to other executives".