He became a trader and merchant in the Far North District of the country, and was later active in business and civic affairs in Auckland.
In March 1840, one month after the signing of the Treaty of Waitangi, he returned to Kororareka and again opened a store.
In March 1841, he went to Auckland and traded land, settling permanently there soon after and establishing a merchant store.
He was a foundation member and supporter of the fledgling Jewish congregation, and with David Nathan secured a grant of land in 1843 on the corner of Karangahape Road and Symonds Street for a Jewish section of the Symonds Street Cemetery, Auckland.
John Israel Montefiore eventually returned via Sydney to London, and died in Hampshire on 14 February 1898.