On 1 May 1707 the Scottish Parliament and the English Parliament each passed an Act of Parliament to simultaneously dissolve and form the new combined Parliament of the United Kingdom of Great Britain.
The new parliament would sit at the Palace of Westminster, the home of the old English Parliament. Previous attempts at union had been made, but this was the first time there was sufficient support on both sides to make it happen.
Put simply, the Scots needed financial support from England, and the English wanted to ensure that Scotland would not choose a different monarch. It was not, however, a universally popular move and many teething troubles had to be overcome as the two different sets of traditions and practice were merged into one parliament.
Robert Burns would famously write about the Scots parliamentarians that had signed the Act of Union:
...O would, or I had seen the day
That Treason thus could sell us,
My auld grey head had lien in clay,
Wi' Bruce and loyal Wallace!
But pith and power, till my last hour,
I'll mak this declaration;
We're bought and sold for English gold-
Such a parcel of rogues in a nation!
Burns’s view, and the view of many Scots, was that the parliamentarians that signed the act had been bribed. Tens of thousands of pounds were sent north to recompense Parliamentarians for losses they would suffer as a result of the union and for pensions.
The 1707 Union of Parliaments would open up the English colonial markets to Scots trade. In time Scotland recovered from the financial disaster of the Darien Scheme and the Scots made the most of the opportunities that the union offered.