The prosecution indicted Lee, the vice chairman of Samsung Electronics Co., in February on charges of providing or promising to give 43.3 billion won ($38 million) to Park and her friend Choi Soon-sil.
In return, he asked for government support for his leadership succession in South Korea's richest conglomerate, according to the prosecutors.
Part of the bribery charges include the sponsorship of equestrian training of Choi's 21-year-old daughter, Chung Yoo-ra.
The prosecution has claimed that, by doing so, Lee secured a crucial vote from the state-run pension service needed for the merger through the president.
Lee is also accused of embezzlement, hiding assets overseas, concealment of criminal proceeds and perjury.
He has argued he never asked for favors from Park and he was not in a position to make a management decision for the group. He has said the merger was spearheaded by the control tower based on the judgment that it's best for the company's long-term future.
Lee is viewed as the de facto head of the sprawling business empire worth 350 trillion won, after his father and Samsung Group patriarch Lee Kun-hee was incapacitated after having a heart attack in 2014.
He also denied he had known of Choi and Chung, and their relationships with the former president, before the scandal broke around October last year.
The Seoul Central District Court is expected to deliver its verdict on Lee before Aug. 27. The ruling will likely have a direct impact on the ongoing trials of Park and Choi who are facing similar charges.
In Lee's final trial, the prosecution is also to request sentencing on four co-defendants -- all Samsung executives, including Choi Gee-sung, former head of Samsung's now-disbanded control tower Future Strategy Office -- for their involvement in the high-profile case.
Choi has defended his boss by putting the blame on himself. He has told the court he handled everything related to Choi and Chung's sponsorship, and that he never fully reported to Lee about the funding. (Yonhap)