He taught in a Glasgow school conducted by his older brother Allan and was recruited for Australia by Dr John Dunmore Lang, who heard him preach in Greenock in 1837.
He was ordained for Australia with his friend James Forbes on 29 June 1837 by the Church of Scotland Presbytery of Glasgow.
He was appointed Chaplain to some 260 immigrants on the Midlothian, which left Portree, Skye on 7 August 1837 and arrived in Sydney 12 December 1837.
Lang falsely represented to Governor Gipps that Lord Glenelg had given public assurances that they would be allowed to settle as a group, which was contrary to the usual policy.
Peter's estate exclusive of runs and licence for over 280,000 acres (1,100 km2) of land was sworn at not less than £25,000, so Mary was exceedingly wealthy.
McIntyre led those who protested and withdrew to form the Presbyterian Church of Eastern Australia in October 1846.
McIntyre was anxious to see a thoroughly orthodox and evangelistic Church but was hampered by the difficulty of securing recruits prior to the discovery of Gold in 1851 and the tensions between Highlanders and Lowlanders.
In 1854 he recruited his brother Allan and James McCulloch, who had married McIntyre's niece, for the PCEA ministry.
McIntyre removed to St George's Church, Castlereagh Street, Sydney and was inducted 20 February 1862.