By signing the confidence and supply deal, the Northern Irish Democratic Unionist Party agreed to support UK Prime Minister Theresa May's Conservative minority government.
"Today we have reached an agreement with the Conservative party on support of the government in parliament. This agreement will operate to deliver a stable government in the United Kingdom's national interest at this vital time," Foster said in a statement.
After the deal was signed, Foster told reporters that the Conservative party had agreed to increase funding in Northern Ireland, bringing one billion pounds (about $1.27 billion) over the course of two years to the country.
"Following our discussions the Conservative Party has recognized the case for higher funding in Northern Ireland, given our unique history and indeed circumstances over recent decades," Foster said. "We welcome this financial support of 1 billion pounds in the next two years."
Foster also revealed that the two parties had agreed to meet NATO spending target.
The United Kingdom held the snap election on June 8, which resulted in a hung parliament as May's Conservative party got 318 mandates, thus failing to secure an overall majority in the House of Commons by falling short of the required 326 seats.
