Simon Easterby will coach Ireland's men's team in the 2025 Six Nations while Andy Farrell takes a sabbatical to lead the British & Irish Lions ahead of their tour to Australia next summer.
Easterby will also coach Ireland on their 2025 summer tour and the Emerging Ireland tour of South Africa in October. He has been part of the Irish coaching setup since 2014 and also won 65 caps as a player. He will take charge from Dec. 1.
IRFU Performance Director, David Humphreys, said: "I am delighted to confirm Simon's promotion later this year and it is recognition of his evolution and high-standing as a coach within the Ireland set-up over the last 10 years.
"Today's announcement ensures a smooth transition and continuity as Ireland looks to build towards an exciting few months ahead. Over the last decade Simon has moved from forwards coach to defence coach and he has played a key role in Ireland's success during that time."
Easterby added: "To be asked to lead the Ireland team is a huge honour and one that I am thrilled to accept. It is the highest achievement of my coaching career to date and I'm looking forward to working with the talented backroom team and players while Andy is away with the British and Irish Lions.
"I have greatly enjoyed being a part of the men's national team journey over the last 10 years and I believe that there are even brighter days ahead as we build towards a huge few months.
"There's a lot to play for before December and we're looking forward to providing the next crop of future Irish players with a chance to impress against talented international opponents in South Africa and then across the four Autumn Nations Series matches at Aviva Stadium."