Addressing a media conference in Delhi, Jaitley said, "late on 30th of June".
The GST, India's most ambitious tax reform, replaces an unwieldy patchwork of tariffs and creates a single economic zone with common indirect taxes - something that neither the European Union nor the United States can boast.
He said, as GST is a more efficient system which is prone to checking evasion, revenues will grow, and spending capacity of Centre and state governments will increase.
The GST Council, that brings together the Central and State Governments, has met 17 times to thrash out how the tax will work.
It would unify the Dollars 2 trillion Indian economy and 1.3 billion people into a single market.
The government will not reconsider the July 1 roll-out date for GST, finance minister Arun Jaitley said on Tuesday, emphasising that the date was announced well in advance and so "nobody had any business not to be ready". "We have got FRBM Act and fiscal deficit target, we intend adhering to it", he said.
"There is still two and a half months to be ready, but if he (business) is still not ready, I am afraid, but he doesn't want to be ready", he said.
Modi and Mukherjee will speak briefly on GST and two short films on the tax regime will be shown, Jaitley said. Under the new system, taxpayers will have to make a self-declaration under a new form for the month of July by August 20 and for August by September 30. Now, trade and industry have to prepare themselves. This will give them extra time of about a month to file returns without worrying about penalties and fines.
"GST is commencing from July 1". The Finance Minister said all states except Kerala and Jammu and Kashmir had endorsed the GST.
"All GST Council decisions have been taken through consensus".
He further said the process of registration on the GSTN is going on smoothly. "The size of the formal economy should also increase".