Timeline: How Narendra Modi made GST a reality

By abandoning confrontation and seeking consensus, Prime Minister Narendra Modi has pulled off his biggest reform yet, securing the unanimous support of both houses of the Parliament for a planned Goods and Services Tax (GST).

Here's a timeline of how Modi and Finance Minister Arun Jaitley first brought India's federal states on board, before finally closing the deal at a series of meetings with an opposition Congress party that had become increasingly isolated.

May 19 - Congress, which suffered its worst-ever election defeat at the hands of Modi in 2014, is punished by voters in a round of regional elections.

June 11 - Further losses in elections to the Upper House mean that Congress and its fellow holdout, Tamil Nadu's ruling party, would struggle to muster the one-third of votes needed to stop a constitutional amendment to enable the GST.

June 15-16 - Jaitley wins the full support of West Bengal, a key swing state. Congress's anti-GST front is crumbling.

July 15 - Jaitley holds formal talks on the GST with Congress party negotiators for the first time in nine months.

July 17 - At an all-party meeting, Modi urges opposition parties to put national interests above all else and back the GST bill.

July 19 - Jaitley holds a second round of talks with Congress. He also meets Bihar Chief Minister Nitish Kumar, who rules in an alliance with Congress. Kumar is placated by a government offer to delay a controversial piece of legislation and his party publicly backs the GST the next day.

July 26 - Jaitley offers to compensate states for five years for all revenue losses arising from the GST. The states are fully on board.

July 27 - Congress proposes tweaks to the GST amendment. They are approved by Modi's cabinet that evening.

July 28 - Two more meetings are held but Jaitley resists a Congress demand to anchor the GST rate at 18 percent.

August 1 - Congress tells Jaitley it will back the bill.

August 3 - The constitutional amendment bill passes the upper house, with 203 votes in favour and none against, after lawmakers from Tamil Nadu walk out.

August 8 - The lower house unanimously approves the amendment.

WHAT HAPPENS NEXT

- At least half of India's states and self-governing union territories need to back the GST amendment.

- The GST Council, a forum bringing together the centre and the states, should draft the key terms and scope of the GST. The government's chief economic adviser has recommended a main rate of 18 percent, but many states want it to be higher while Congress wants it to be capped.

- Two new GST bills are expected to come before parliament in the winter session that begins in November. The states, too, are required to pass their own GST bills.

- The government targets a GST launch date of next April 1, the start of India's financial year, although experts say that deadline is likely to slip.