In 1964, the Sisters of Mercy in Christchurch, Aotearoa New Zealand established a house in Lapaha, Tonga. Four sisters went to Tonga. The founding sisters taught in school, worked with the villagers in raising crops and pigs, and ministered to the people in a host of ways. In 1991, a second house was opened in Kolonga.

Today sisters in communities at Kolonga and Lapaha are engaged in secondary school teaching, parish work, support for women and children, prison chaplaincy and justice and development programmes. The Sisters of Mercy work closely with Caritas on education, justice, and development programmes.

Caritas Tonga has played a vital role in coordinating relief and rehabilitation projects over the years, such as the construction of cyclone-strength housing for vulnerable families. Through projects such as the Tonga Community Development Programme, Caritas Tonga is working to restore dignity to families with low incomes and to unemployed young people so that they can eventually become self-reliant. The beneficiaries run the projects so that young people are employed in initiatives of their own making, thereby ensuring long-term sustainability.