"If they announce it now, it will come online in 2015," he told an economic forum.
Irwan said the sales tax rate, previously mooted at 4 percent, hasn't been decided yet. Staple foods such as rice and milk powder will be exempted to ease the burden on the poor, he said.
The government previously said a 4 percent GST could boost its revenue by 1 billion ringgit ($302 million) annually and help cut reliance on income from state oil company Petronas.
The confidence boost from plans for a new tax regime could also help dampen capital outflows. Malaysia and other Asian nations have come under stress as China slows and investors anticipate a scaling back of monetary stimulus in the U.S. The Malaysian stock market has slid while the local ringgit has lost nearly 7 percent since April.
The GST is expected to replace the current narrowly applied 10 percent sales tax and five percent services tax. The GST will be levied on transactions at all stages of production of goods and services. Malaysia's current sales and services taxes are single-stage taxes applicable to selected goods and services
Irwan said the government will also announce plans to rationalize subsidies for fuel, food and other items next month so they benefit the poorest rather than being broadly applied.
With the new tax regime, he said the government is confident of trimming its fiscal deficit to 3 percent of gross domestic product by 2015 and hit a surplus by 2020.
"Hopefully if there is no major recession ... we will be on target to achieve a surplus in 2020," he said.