He served as a member of the Legislative Assembly from 1958 until his death, had two spells in the cabinet between 1962 and 1965, and became the first official Leader of the Opposition in 1968.

[4] Shortly afterwards he was also defeated in a vote to become the Speaker, losing to Teariki Tuavera.

[5] After Julian Dashwood was sacked from the cabinet in 1964, Brown appointed Matepi as his replacement, giving him the portfolios of Health and Social Development.

He was re-elected in 1968 as a United Cook Islanders candidate, after which he became Leader of the Opposition,[7] serving for a year before handing over to Tangaroa Tangaroa as part of an agreement to rotate the post between the party's MLAs.

In 1977, Matepi was awarded the Queen Elizabeth II Silver Jubilee Medal.