On Lafley's appointment, Ackman told CNBC: "A.G. Lafley is one of the greatest CEOs and we're delighted to have him back."
In a statement released Friday, Ackman said: "A.G. is a legendary CEO. We expect that he will quickly make progress to accelerate the turnaround of the business. This was the right move by the board."
During McDonald's tenure the stock was up 54 percent, but that underperformed the S&P 500's 80 percent advance. It also lagged other consumer product companies.
In January, the company reported better than expected earnings and revenue, a performance that was seen as giving McDonald some breathing room.
(Read more: Procter & Gamble Tops Estimates, Raises Outlook)
The strong results prompted CNBC's Jim Cramer to predict P&G could be the "best stock in the Dow." He also praised McDonald for answering his critics. "I like this guy, he means business."
Analyst Ali Dibadj told Dow Jones he thinks Lafley is a "great CEO." While McDonald's departure wasn't expected, Dibadj said, "Clearly the Board had had enough."
P&G also confirmed its previous fiscal year and fourth quarter guidance. Its fiscal year ends on June 30.