A rolling road closure will be in place on St Mary Street from 1200 until 1430 BST to allow the revellers through.
Music stars including the Magic Numbers and Jimmy Cliff will also be playing the three day festival which takes over the city's civic centre from Friday.
The free event, which also features a fairground, may attract 250,000 people.
The year's musical line up has been described as "incredibly strong" by organisers, who said they were pleased to have secured London band the Magic Numbers for the Sunday night headline slot.
They were nominated for the Mercury Music Prize in 2005 for their eponymous debut album and recently recorded She's Leaving Home for BBC Radio 2's 40th anniversary celebration of the Beatles' album Sgt Pepper's Lonely Hearts Club Band.
"The Magic Numbers have been playing just about every festival going this summer but this is the only one they are doing for free," said a Cardiff Festival spokesman.
Big Weekend line up
Headlining on Friday will be double Grammy award winners Soul II Soul, who had hits in the late '80s with Keep on Moving and Back To Life.
On Saturday, actor and reggae singer of classics including The Harder They Come and Many Rivers to Cross, Jimmy Cliff tops the bill.
It will be the first time the annual Cardiff MAS carnival has paraded through the city as part of the Big Weekend celebrations.
The parade leaves from the Canal Path Park in Butetown at 1200 BST on Saturday and will go through Bute Street, The Hayes and onto the City Hall lawn at 1400 BST.
It will feature costumes created at carnival arts workshops run by South Wales Intercultural Community Arts (SWICA).
Councillor Nigel Howells, Cardiff council's executive member for sport, leisure and culture said: "The Big Weekend is a hugely popular event in the summer calendar, and we've made it even more attractive this year by involving the Cardiff MAS Carnival.
"It will bring the great spirit of carnival and the results of a lot of hard work to a much wider audience in the city centre."
No alcohol, glass bottles or cans will be allowed onto the fairground site of the Big Weekend, which has been designated an alcohol free zone.
Bars will be open on site and revellers are urged to bring any soft drinks in plastic bottles only.
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