TV3 is to screen the Six Nations Championship from 2018.
The station will broadcast all games from the championship, as well as highlights, preview and magazine shows.
2017 will mark the Six Nations' final season on RTE, before switching to TV3 for four years.
TV3 also won the rights to host this year's Rugby World Cup.
"We are delighted to be working with TV3 on developing the interest in the Championship and to ultimately grow this wonderful competition in Ireland," said CEO of Six Nations Rugby John Feehan.
"TV3's coverage of Rugby World Cup was very successful and we believe that they will inject new and exciting ideas in the broadcasting of the Six Nations Championship.
"I wish to acknowledge the excellent work and support of RTE in the coverage of the RBS 6 Nations Championship over the years, and indeed we look forward to working with them for the remaining two years of the existing contract."
RTE expressed their disappointment in a statement.
They said: "This is extremely disappointing news for RTÉ. We have a long and proud tradition of showcasing the 6 Nations and putting our heart and soul into our coverage.
"We want to assure the Irish public that every possible effort was made by RTÉ to retain these rights. As a public service broadcaster, RTÉ’s ambition has always been, and continues to be, to deliver the best possible viewer experience and to share moments of major national importance.
"We put forward the best possible bid within our means, while always mindful of the significant responsibilities attached to spending public funds.
"We have a phenomenal year ahead in 2016, with the GAA Championships, the Olympic Games and Euro 2016. We also look forward to delivering the 6 Nations Championship in 2016 and 2017.
"Along with the range of Sports we have already secured and are delivering, we will look to other opportunities in Irish and international sports and remain committed to delivering a comprehensive portfolio of Sport to the Irish public."
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