An official said parliament would sit on the day regardless of whether Boris Johnson is able to win an agreement from EU leaders on a Brexit deal.
On Saturday, Johnson also will be forced to ask the EU to delay Brexit under the Benn Act, if no deal has been approved by Parliament and they have not agreed to the UK leaving without an agreement in place.
Parliament has passed a law to force Johnson to seek a Brexit delay if he fails to negotiate a new deal with the EU at a summit on October 17 and 18, Presstv Reported.
The summit in Brussels is the last scheduled meeting of leaders throughout the bloc before Britain is set to leave on October 31.
But the Prime Minister has vowed he will not extend the Brexit deadline, and that Britain will leave the EU as planned on 31 October "do or die".
The government source said if a deal has not been reached by the Saturday session of Parliament, a series of votes could be held on the day to decide on possible ways forward.
This is the first Saturday sitting in the UK Parliament in 37 years. The last time was during the Falklands War in 1982 and before that, the Suez Crisis of 1956.
19 October will also likely see thousands of protesters descend on parliament calling for another referendum to give the public a "final say" on Brexit.
In a statement, the Labour MP Jess Phillips said: “The 19th of October was already set to be a historic day, with hundreds of thousands of people coming to London to demand that the final decision on Brexit is not made by Boris Johnson but by all of us.
With the news that Boris Johnson is planning an emergency session of parliament on the same day, there could not be a more important moment for everyone who cares about our country and our future to march, and to insist that we are all given the final say.”