Q&A: The Lisbon Treaty. The Lisbon Treaty became law on 1 December 2009, eight years after European leaders launched a process to make the EU more democratic, more transparent and more efficient.Under EU rules, the treaty had to be ratified by all 27 member states before coming into force.The last country to ratify the treaty was the Czech Republic, which completed the process on 3 November 2009.he Lisbon Treaty which succeeded it was rejected by Irish voters in June 2008. But it got overwhelming support in a second referendum in the Irish Republic on 2 October 2009.