The body of Bush Senior, which has been lying in state at the US Capitol, will be moved to the National Cathedral later on Wednesday for the funeral.
His son, former President George W. Bush, as well as former Canadian Prime Minister Brian Mulroney, former US Senator Alan Simpson and presidential historian Jon Meacham, the late President's biographer will deliver eulogies.
Bush Sr, who served as the 41st US President between 1989 and 1993, died last Friday at the age of 94. He will be buried in his home state of Texas, alongside his wife, Barbara.
Former leaders, including John Major, who was UK Prime Minister for most of Bush Sr's term, were also expected to attend the funeral.
Another departure ceremony was due to take place at Joint Base Andrews in Maryland. Bush Sr's casket will be taken on the presidential plane dubbed "Special Mission 41" for the funeral process back to Texas.
His casket will then be taken to St. Martin's Episcopal Church in Houston, where the body will lie in repose.
A second service was scheduled for Thursday, after which his body will be taken via a train bearing his name to his final resting place at the George H.W. Bush Presidential Library in College Station, Texas, 160 km from Houston.
He will be buried besides "the love of his life", as he always defined his wife Barbara.
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