Tyson took a red-eye flight overnight from Las Vegas to Louisville, Ky.
According to Ali family spokesman Bob Gunnell, Tyson was highly emotional when he learned of Ali's death and wasn't sure if he could handle the memorial.
Other pallbearers include actor Will Smith and former heavyweight champion Lennox Lewis, along with other family members and friends -- including Jerry Ellis, the brother of Ali's former sparring partner and heavyweight champion Jimmy Ellis. Smith portrayed the legendary boxer in the 2001 movie "Ali" that earned him an Oscar nomination for Best Actor.
Ali died June 3 at the age of 74 from septic shock after being hospitalized with a respiratory condition.
A 19-mile processional that will wind through the boxing legend's hometown gets underway Friday morning. The procession will tour landmarks in Ali's life, including his childhood neighborhood and the gym where he began his boxing training.
An interfaith public memorial service follows at the KFC Yum! Center as thousands pay their final respects. Former President Bill Clinton will deliver the eulogy, and among the speakers will be sportscaster Bryant Gumbel, comedian Billy Crystal and Ali's wife, Lonnie.
On Thursday, the Jenazah, a traditional Muslim funeral prayer service, was held at Freedom Hall in Louisville. After the public prayer service, Ali's family observed a private funeral.