The Philadelphia-based businessmen helped initiate this week's trip to the city by two members of Ireland's Western Development Commission.
Lisa McAllister and Joanne Grehan, who are based in the Commission's offices in Roscommon, are meeting with businessmen and politicians through Friday evening.
Councilman James Kenney will hold a press conference on Thursday about the visit from the WDC, which is a state agency responsible for development in the five counties of Connacht as well as Clare and Donegal.
"We've been in conversation with them since early February," said Hegarty. "We were in Ireland two weeks ago and we met with them then. We have two clients who are interested in going over to Ireland."
The new firm's website says: "Maguire Hegarty, LLC is a full service accounting firm serving clients in the Greater Philadelphia area and internationally, with a specialty in working with companies associated with Ireland and the United Kingdom."
"We've been friends for 20 years," said Hegarty, who was born in the United States but raised in Counties Donegal and Meath. "We're pooling together their different talents and areas of expertise,
"Our business networks were a little different," added Hegarty, a partner in the accountancy firm Parente Randolph until recently.
"It made sense. We didn't want to say in 10 years, 'we should have tried it.'"
Maguire, who is a graduate of Trinity College Dublin, first came to Philadelphia in 1981.
"The older guy's name goes first," he said, laughing. "But phonetically, it works better."