The new role includes the coaching of the national team's scrum as well as being involved in the National Scrum Development Programme.
Through the National Scrum Development Programme, Greg will be working with the provincial and underage scrum coaches to identify and develop scrum talent and will focus on improving players' general understanding of scrum mechanics and technique.
He won 10 caps for New Zealand between 1999 and 2001 and played Super Rugby with the Canterbury Crusaders. Before joining Leinster, he held the role of scrum resource coach for the Wellington Hurricanes franchise.
Ireland head coach Joe Schmidt commented: "Greg played an important role during the Six Nations and the national coaching staff are delighted that he will be joining us on a full-time basis. He will also be a valuable addition to the National Scrum Development Programme."
Greg Feek said: "I am excited to be taking on this new role. I have thoroughly enjoyed my time working with Leinster and have grown as a coach at the province.
"There is some good scrum talent across all four provinces but there is always plenty to work on as we attempt to maximise the growth and development of the emerging talent while also staying as competitive as possible at the top level."