Barrett was born and raised in the slums of either Durham or Bermondsey, England He spent six years as a sailor and arrived in Taranaki from Sydney as a mate on the trading vessel "Adventure" in March, 1828. He and captain John Agar "Jacky" Love established a trading post at Ngamotu (site of modern-day New Plymouth), trading muskets and trinkets for flax, maize, wheat and vegetables grown by local Te Atiawa Māori. The trading post attracted increasing numbers of passing ships.