MacKay announced he is not running for re-election this fall, but did not close the door to returning to politics some day.
But at this moment, he told supporters at a museum in his riding of Central Nova, he wants to put his focus elsewhere.
"I love what I do and I love the opportunities it afforded me to help others but simply put, I love my family more," he said.
MacKay, who turns 50 this fall, is expecting a daughter, his second child, later this year with his wife Nazanin Afshin-Jam, a human rights activist he wed three and a half years ago.
While he has spent nine years in cabinet introducing Prime Minister Stephen Harper at events, the tables were turned Friday as Harper rose to introduce him.
Harper described himself as filled with "tremendous pride and more than a little sorrow," looking close to tears as he delivered a heartfelt tribute to his longtime political lieutenant.
"Peter MacKay is an outstanding public servant," Harper said. "Peter MacKay is a great person. And Peter MacKay is a historic figure."
It is the history the two men share together that prompted Harper to travel to Nova Scotia on Friday — MacKay was at the helm of the Progressive Conservative party when it merged with the Canadian Alliance.
"That moment in October 2003 changed, without a shadow of a doubt, the course of Canadian politics," Harper said.
"It took a sense of destiny, it took a spirit of humility and it took a willingness to compromise. These were difficult decisions, truthfully for reasons I won't revisit, more difficult on Peter's side of the ledger than mine."
MacKay chose not to challenge Harper for the leadership of the newly formed Conservative party and while that earned him the loathing of many former PCers, his loyalty to Harper was never forgotten.
When the Conservatives formed government in 2006, MacKay immediately had a spot in cabinet, first at Foreign Affairs, then Defence and finally, Justice.
It was a full-circle move for MacKay, who was motivated to join politics after working as a criminal prosecutor in Nova Scotia.
"As part of life's rich pageant for a small town boy like me, this has been more than I ever imagined," he said.
Harper was told weeks ago of MacKay's decision and his presence Friday spoke volumes about the fact little political rancour exists between the two men. The relationship is so close, MacKay's son celebrated his first two birthday's at Harper's home.
Whether MacKay may some day seek to occupy 24 Sussex will continue to be a source of political speculation.
He said Friday he will remain in cabinet and as an MP until the fall election, but then seek work in the private sector, though he's accepted no positions yet.
But a return to politics isn't off the table.
"This is not goodbye, this is farewell," he said. "See you soon."
MacKay pledged to remain an active part of the conservative movement and there's little doubt his heft will be needed on the campaign trail.
His departure leaves Scott Armstrong as the only Tory incumbent running for re-election in Nova Scotia this fall.
MPs Gerald Keddy and Greg Kerr announced months ago they would not run again.
The Tories only hold four seats in the province. The NDP have three and the Liberals four.
"It certainly ... gives us a better chance in his old riding come the next election," said Liberal MP John McCallum, while also wishing MacKay well.
Polls suggest the Liberals have the lead in the province going into the fall campaign, with the Conservatives in second.
There are 30 Conservatives not seeking re-election this fall, including cabinet ministers Christian Paradis and Shelly Glover.