Smith, who portrayed Ali in the 2001 film about the boxer’s life, and Lewis will be among up to 15,000 people due to attend the funeral service in Ali’s home town of Louisville, Kentucky on Friday.
The other pallbearers include Jerry Ellis, the brother of Ali’s sparring partner and former world heavyweight champion Jimmy Ellis, Ali’s cousin John Grady, his nephew Ibn Ali, his former brother-in-law Komawi Ali, Ali’s cousin Jan Wadell and family friend John Ramsey, a spokesman for the Ali family said.
Former US president Bill Clinton, Turkish president Recep Tayyip Erdogan and King Abdullah II of Jordan are expected to address the service at the KFC Yum! Centre, which will be open to the public and live-streamed on the internet.
Malcolm X’s daughter Attalah Shabazz, Ali’s wife Lonnie Ali, his eldest daughter Maryum and US actor Billy Crystal are also among the speakers.
Ali, a three-time world heavyweight champion, died in hospital in Arizona last week. He was 74.
His funeral will be preceded by a Jenazah, an Islamic funeral prayer programme, which will also be open to the public on Thursday at the Freedom Hall, where Ali made his professional debut with victory over Tunney Hunsaker in 1960.
Family spokesman Bob Gunnell said 14,000 tickets will made be available to the public for the Jenazah.
“Everything that we’re doing here was blessed by Muhammad Ali, and was requested,” Mr Gunnell said.
“He wanted the memorial service to reflect his life, and how he lived.
“He wanted everyone to be able to attend. He was the people’s champ, and he wanted the memorial service to reflect that.
“We want this to be inclusive of everyone. That’s why we set Freedom Hall, not just with its historical significance, but with the size of Freedom Hall, so that everyone fits in.
“That Muslims and people of all faiths could attend, and perhaps learn more and be like Muhammad Ali, and open their hearts to everybody.
“This is not a political statement, this is not about politics, this is about how Muhammad Ali lived his life.”
Ali, formerly named Cassius Clay, died of septic shock due to “unspecified natural causes”, Mr Gunnell said.
He had been admitted to hospital earlier in the week with a respiratory condition having lived with Parkinson’s disease for 32 years.