Admiral, Wales' only FTSE 100 listed company, first appeared on the national team's jersey in 2010, and the two-year extension to the existing deal will take the partnership through to the 2015 World Cup.
WRU chief executive Roger Lewis said: "We are delighted to be able to welcome Admiral on board for a further two years."
He added: "It is always pleasing when a partner is interested in renewing sponsorship, it tells us we are doing something right and it is testament to the power of the WRU brand that a major company in Wales is now signed up with us until 2015."
