These included bribery, embezzlement and hiding assets overseas.
What did he do?
The 49-year-old is accused of giving donations worth 41bn won ($36m; £29m) to non-profit foundations operated by Choi Soon-sil, a friend of South Korea’s former President Park Geun-hye, in return for political favours.
Prosecutors said the donations were made to Ms Park’s confidante to win government support for a big restructuring of Samsung that would strengthen Lee’s control over Samsung Electronics.
But Lee’s defence team said that the payments were signed off without his knowledge.
Lee has previously admitted that the firm also gave a horse and money to help the equestrian career of Choi’s daughter, Chung Yoo-ra, but denied seeking favours.
On Friday, two other Samsung executives, Choi Gee-sung and Chang Choong-ki, were also convicted in the same trial as Lee and sentenced to four years in prison. Former Samsung Electronics president Park Sang-jin and executive vice-president Hwang Sung-soo were handed suspended sentences.
Will Lee serve time in jail?
Analysis – by the BBC’s Yogita Limaye in Seoul
This isn’t the first time a top executive of a big conglomerate has been convicted for corruption in South Korea.
But in the past, they’ve either been given suspended sentences or have been pardoned by the president.
The new president, Moon Jae-in, has already said there will be no more presidential pardons.
So if Lee’s sentence is upheld by higher courts and he ends up serving his complete sentence in jail or a significant part of it, that will be a departure from what we’ve seen in South Korea in the past.
And the new government says that will be a strong message to chaebols that they need to clean up the way they do business.
What does it mean for Samsung?
The conviction represents a huge blow to South Korea’s biggest and most well-known business empire. Since the verdict, Samsung shares fell by 1%.
It also raises questions about the future leadership of the family-run conglomerate. Lee has been standing in as chairman since his father, Lee Kun-hee, suffered a heart attack in 2014.
Lee has two sisters, who are in management roles in different parts of the Samsung group, but it is unclear whether they could be brought in to higher positions.
Since Lee’s arrest six months ago, the group’s business operations have continued largely unaffected.