McDonald began his NHL broadcasting career in 1967, as the original voice of the expansion Los Angeles Kings. Initially, the Kings considered pairing him with a then-unknown Al Michaels. Although "Jiggs" had been McDonald's childhood nickname, he had never used it professionally, nor at all among those he'd come to know after becoming an adult, instead going by "Ken", a shortening of his middle name. However, when he was hired by the Kings, the team's then-owner Jack Kent Cooke demanded that McDonald identify himself to listeners with a nickname that would be more memorable than simply "Ken McDonald". McDonald objected to the use of the nickname, but Cooke was insistent. After five seasons with the Kings, he joined the Atlanta Flames, also as that team's original announcer, with Bernie Geoffrion serving as his broadcasting partner. The Flames' ownership offered to allow him to drop the "Jiggs" nickname, but he opted to keep it since it was by then well-established as the name by which he was known professionally. When the Flames moved to Calgary in 1980, he joined the New York Islanders broadcast team as play-by-play announcer, replacing Tim Ryan; former Islanders captainEd Westfall was the color commentator. He spent 15 seasons as the Islanders' play-by-play man, and the team won three Stanley Cups during the period, and advanced to another Final. Including national work, as well as work for other teams, he called the play-by-play of over 200 NHL playoff games. In 1988, when the New Jersey Devils eliminated the Islanders from the playoffs, he did play-by-play on New Jersey Devils telecasts, partnering with Peter McNab. Although he was not the announcer for the first Stanley Cup championship team, he hosted the New York Islanders' 25th anniversary celebration in 1996. In future years, he did play-by-play on Toronto Maple Leafs telecasts and Florida Panthersradio broadcasts. In November 2003, he announced his 3,000th regular season game; his number of games called is thought to be the highest by an NHL announcer. Following the 2003–04 season he retired, but he substituted for Dave Strader when the latter was on NHL on NBC assignments on Panther telecasts during the 2005–06 season. Since the 2006–07 season to 2016–17 season, he has returned to call Islanders games on MSG Network, filling in for Howie Rose. With his Islanders work in 2010, he has called hockey games across six decades. With Rose broadcasting the Mets playoffs in 2015, McDonald filled in for the first 3 games of the 2015-2016 season. He also did broadcasts on nationally televised NHL games for numerous networks. Notably, he called games for SportsChannel America for five years, during which the channel was the rights-holder for national NHL telecasts with Herb Brooks or John Davidson. In addition, he broadcast the Winter Olympics for ABC and TNT, calling at three Games. In addition, he filled in for Florida Panthers radio play-by-play man Randy Moller for three games when Moller became ill in January 2010. He returned in 2017 and call the Islanders' and Kings' games, both against the Panthers on January 11, and February 9, respectively.
In late October 2008, McDonald and his wife were vacationing in Asia, only to be stranded in Bangkok, Thailand in late November and early December for a week in the wake of the 2008 Thai political crisis that resulted in the takeover of two commercial airports in Bangkok by pro-democracy activists.
