Hundreds of volunteers in Sri Lanka have been scrambling to complete the project which is situated on a popular beachside promenade in Colombo.
The metal frame of the tree will stand at 98 metres (320 feet) high, which will break the current record holder by 40 metres (131 feet).
More than one million natural pine cones will be attached to the frame, topped by a 6-meter-high (20-foot-high) shining star.
Organisers hope that the tree will promote religious harmony in the Buddhist-majority country.
"This is just to show the world that we can live as one country, one nation," said the organiser and former cricket player Arjuna Ranatunga.
Currently, the record for the tallest fake tree is held by a Chinese firm that put up a 55-metre-high (180 t) tree in the city of Guangzhou last year.
Attempts to complete the project in time for Christmas Day had been blighted by critics.
In November, Cardinal Malcolm Ranjith - representing the island nation's 1.5 million Catholics - said the £64,000 project as a waste of money and caused the venture to be temporarily suspended.
Prime Minister Ranil Wickremesinghe called for work to begin again and said the tree was not being built with public money, but with donations from individuals and private firms.
The delay caused workers to miss initial deadlines set for 15 December and then another today.
Organisers are hoping to have the tree up by Christmas Eve. The tree is meant to stay up until January 6.