He is the former CEO of Stryker Corporation, another medical device manufacturer headquartered in Kalamazoo, Michigan.
MacMillan received a B.A degree in Economics from Davidson College, where he was co-captain of the golf team.
[5] In December 2013, following a settlement with activist shareholder Carl Icahn, medical technology company Hologic named MacMillan their president and chief executive officer.
[6][7] In the aftermath of the forced disappearance of Chinese women's tennis player Peng Shuai, Macmillan expressed support for the Women’s Tennis Association (WTA) as the organization cancelled its events in China.
He negotiated a multiyear sponsorship deal with WTA, including Hologic becoming the title sponsor of association.