The 30-year-old former Sheffield Eagles player has made 223 appearances for the Rhinos since joining in 1999, and scored 1234 tries on his way to becoming Super League’s most prolific try-scorer of all time.
Leeds boss Tony Smith said that it was “great that Keith is extending his commitment to the club”.
"He has made Leeds his home over the years and wants to continue his career with us. He has shown in the Tri Nations that he is still at the top of his game and I would expect him to continue to do be up there for the foreseeable future because he is such a powerful and athletic individual."
Senior said: "I am delighted to have agreed a contract extension. I had one year remaining on my previous deal but I had no hesitation in signing the new contract when the club offered me it.
"The Rhinos are a special club and I feel privileged to have played for them and hopefully over the coming years we can fulfil the potential that is here at the club and give the fans the success they deserve."