The charismatic Ali, a dazzling fighter and outspoken civil rights activist who became one of the 20th century’s towering figures, died Friday at age 74 after health problems complicated by a long battle with Parkinson’s disease.
Smith, who played the title role in Michael Mann’s film “Ali” (2001), became close to the boxing legend after the filming.
Lewis, who was born in Britain, is considered one of the greatest boxers of the last 25 years, having won several world titles in the 1990s and 2000s.
The two celebrities will carry Ali’s coffin together with six family members and close family friends, family spokesman Bob Gunnell said.
The funeral ceremony is set to take place on Friday in Ali’s hometown of Louisville, Kentucky in front of a huge crowd. It will be broadcast around the world.
Former president Bill Clinton, comedian Billy Crystal and Turkish President Recep Tayyip Erdogan are among those due to speak Friday at the public memorial in a sports arena in the Kentucky hometown of the three-time world heavyweight champion.
The funeral will follow a procession through the streets and will be preceded on Thursday by a family funeral and an Islamic prayer service held in the 18,000-seat Freedom Hall.
The Louisville funeral is aimed at sending a universal message of peace and tolerance, according to organizers.
Ali died in Phoenix, Arizona, where he had recently lived. His body was returned to Louisville by private plane on Sunday.
He will be buried at Louisville’s Cave Hill Cemetery.