The Labour Party leader said he is “delighted that these vital reforms have passed” after they were backed by 53.67 per cent to 46.33 per cent on September 26.
He continued: “They represent a major step forward in our efforts to face the public and win the next general election.
“This is a decisive and important day in the history of the Labour Party.”
Sir Keir also promised to tackle anti-Semitism in the party after closing the door on what he called “a shameful chapter” in its history.
“I want to acknowledge the courage of all the people who spoke up against it,” he said.
“As I promised when elected as leader, the Labour Party is now relentlessly focused on the concerns of the British people and offering them a credible, ambitious alternative to this government.
“This is a crucial step forward for party I lead and am determined to see in government.”
The politician pledged to set out ideas in the coming days on how the Labour Party plans to win the next election.
Earlier on Sunday, Sir Keir watched on as party members bickered over his attempts to reform the internal rules.
He had already been forced to water down his proposals for electing his successors in the face of opposition from unions and the left of the party.
And further criticism emerged as the plans were put before delegates at the party’s conference in Brighton.
Under the original proposal, the one member, one vote system would have been replaced with a return to the electoral college made up of the unions and affiliate organisations, MPs and party members - each with an equal share.
Those plans were abandoned with the revised proposals including a requirement for leadership election candidates to have the support of 20 per cent of MPs, up from the current 10 per cent.