A prolonged investigation into the latest political scandal could potentially derail succession plans at Samsung.
"I will earnestly tell the truth to the prosecutors today", Lee told reporters Monday morning before meeting with prosecutors.
Investigators had sought to arrest Lee when they summoned him last month, but a court ruled there wasn't enough evidence to justify Lee's arrest at that point.
It is alleged he pledged 43 billion won (35 million euros) to a business and organisations backed by an influential friend of the South Korean president in exchange for political support for the merger of two Samsung companies.
But since his father, Lee Kun-hee, suffered a heart attack in 2014, he is considered de facto boss of the entire Samsung Group conglomerate.More news: Congressional Hispanic Caucus requests meeting with ICE officials after raids
The head of Samsung, who first gave evidence in front of a parliamentary hearing in December a year ago, admitted giving $17.46 million (20.4 billion won) to the two foundations.
South Korea's Constitutional Court is hearing arguments in its case to decide whether to uphold parliament's impeachment of Park, who has been stripped of her powers pending the verdict.
Ms Choi is on trial for charges including corruption and coercion.
Lee is suspected of providing financial assistance to President Park's longtime confidante Choi Soon-sil, who is at the center of the presidential scandal and now is in custody, and making donations to two nonprofit foundations Choi controlled in return for getting help in the 2015 merger of two Samsung affiliates.