He has been an advocate for Irish-American causes and American involvement in the Irish peace process, including acting as a key intermediary between Sinn Féin leader Gerry Adams and President Bill Clinton.

He was lead counsel in numerous successful class action cases based on federal Constitutional and statutory claims.

He also lobbied on behalf of low income clients in the Connecticut legislature and helped draft landmark Landlord-Tenant reform legislation.

On a national level, Morrison was a leader of the Project Advisory Group representing the legal services programs from around the country.

In 1982, Morrison mounted a successful grass roots campaign for Congress in Connecticut's 3rd congressional district.

He was deeply involved in human rights issues, visiting Cuba to demand the release of prisoners, Chile as part of a campaign to oust dictator Augusto Pinochet, South Africa to protest apartheid, Nicaragua to oppose aid to the Contras and Paraguay to observe elections after the overthrow of dictator Alfredo Stroessner.

In an interview with Bill Whitaker on CBS News' 60 Minutes broadcast on March 19, 2017, Morrison commented: "The H-1B has been hijacked as the main highway to bring people from abroad and displace American workers.

The incumbent Democratic Governor, William O'Neill, had become very unpopular due to years of state budget crises and chose not to seek re-election.

Morrison, O'Dowd, Bill Flynn (former CEO of Mutual of America Insurance Co.), Philanthropist Chuck Feeney, and Joe Jamison and Bill Lenahan of the Irish American Labor Coalition were crucial in paving the way for Adams's controversial visa into the U.S. in February 1994 to address the National Committee on American Foreign Policy and for the Provisional Irish Republican Army's (IRA) ceasefire declaration of August 1994.

Morrison continued to play an active role in the Peace Process throughout the 1990s and conducted negotiations leading to the renewed IRA ceasefire in 1997.

Morrison's role in the peace process is detailed in the 2016 book Peacerunner written by Penn Rhodeen.

After leaving the Finance Board in July 2000, he founded the Morrison Public Affairs Group (MPAG), a Bethesda, Maryland-based lobbying firm.

In 2008, Morrison appeared at the National University of Ireland, Galway to participate in a debate on the 2008 U.S. Presidential election in support of Senator Barack Obama.

[5] In 2019, Morrison alongside a number of other Irish American political and civil society figures founded the bipartisan Ad Hoc Committee to Protect the Good Friday Agreement.