The Archbishop of Canterbury will lead a short service before Westminster Hall is opened to the public for the Queen's lying in state.
Archbishop Justin Welby will be accompanied at the service by the Dean of Westminster.
It is expected to last around 20 minutes.
After the service, the hall will be opened to members of the public to come in and pay their respects over the next four days.
The government published the full queue route on Tuesday, stretching around five miles along the Thames from Albert Embankment to Southwark Park.
It is believed around a million people will turn out to pay their last respects, with queuing times possibly peaking at 35 hours.
Only around 400,000 people are expected to be able to file past, meaning up to 600,000 people could be turned away.
Churches along the route are reportedly being asked to offer practical assistance to people waiting in line.
The Queen's coffin returned to Buckingham Palace last night from Scotland, where hundreds of thousands of people came out to pay their respects.
A short service was held the coffin's arrival, attended only by close family members.
Today, the royal family will walk behind the coffin as it is taken from Buckingham Palace to Westminster Hall in a solemn procession through central London.
