Prof Malcolm, who holds the Gerry Higgins Chair of Irish Studies at the University of Melbourne, gave a lecture on "Migration and Mental Health: the Case of the Irish" at the University of Otago this week.
The lecture was hosted by the Otago University Centre for Irish and Scottish Studies, and opened an international symposium on migration, ethnicity and mental health.
Prof Malcolm said that, from the 1840s onwards, Irish immigrants and their children had filled mental hospitals in the United States of America, England and Australia "in hugely disproportionate numbers".
"At the same time, Ireland itself had among the highest rates of psychiatric institutionalisation in the Western world."
Early Irish immigrants to Victoria, Australia, had arrived as individual men and women, and not as family groups.
Such immigrants were often poor, the men often working in rather anonymous labouring jobs, having come in many cases from rural areas where local families had known one another for generations.
The migrants were subsequently often working in overseas towns or cities where they became isolated, "very rootless" and alienated, having had to travel extensively in search of manual work.
And they sometimes experienced prejudice, as Catholics in a predominantly Protestant society.
"That's terribly difficult to deal with for anybody," she said.
If today's immigrants, refugees and asylum seekers also felt alienated, not fully accepted or valued in their new homelands, they and their children could also face mental health problems, she said.