Ken Daneyko was selected 18th overall in the 1982 NHL Entry Draft by the New Jersey Devils. In 1980-81, at the age of 16, Daneyko had played for the WHL's Spokane Flyers and scored 19 points as a major junior rookie. In 1981-82, he split the year between the Spokane Flyers and the Seattle Breakers, scoring 35 points in 64 games between the two teams. In 1982-83, he scored 17 goals and 60 points for the Breakers and in 1983-84, he played 19 WHL games for the Kamloops Oilers.
Daneyko made his NHL debut on October 5, 1983 against the rival New York Rangers and scored his first goal against the Penguins on October 30. After playing in just one NHL game the following season, Daneyko played 44 games in 1985-86. The 1986-87 season was the breakout year for Daneyko, who gained a full-time position with the Devils. In 1987-88, he helped the franchise to an 18-point improvement to make the playoffs for the first time in eleven years and the first time since the team moved to New Jersey from Colorado. In the playoffs, the Devils advanced to the Wales Conference finals before losing to the Boston Bruins.
In 1993-94, Daneyko helped the Devils set new team records with 47 wins and 106 points. In the playoffs they reached the Eastern Conference finals before losing a very close series to the New York Rangers, the eventual Stanley Cup champions. It was apparent the team was on the cusp of becoming champions, and they followed through the very next year. After a tough Eastern Conference final against the Philadelphia Flyers, the Devils swept the Detroit Red Wings in the Stanley Cup finals.
Perhaps the biggest shock came the following year, when the star-studded team failed to make the playoffs. On December 8, 1998 Daneyko became the franchise's all-time leader with 935 games played. In 1999-00 the Devils finished second in their division with 45 wins and 103 points. On October 29, Daneyko played in his 1,000th game. In the playoffs, the Devils defeated the Philadelphia Flyers to win the Prince of Wales Trophy in the Eastern Conference. In the championship round, Daneyko played an instrumental part in the Devils winning their second Stanley Cup, besting the Dallas Stars. It was also satisfying from an individual point of view, with Daneyko being awarded the Masterton Trophy for his perseverance, sportsmanship and dedication to hockey.
In 2000-01, the Devils won the Atlantic Division and made it to the Stanley Cup finals to defend their championship of a year earlier. However, the Colorado Avalanche came away with their second Stanley Cup in five years.
As Daneyko entered his 20th season with New Jersey in 2002-03, he continued to to keep his game simple, using strong play in his own end and using his veteran leadership skills to keep his teammates focused throughout the regular season and post season. Daneyko and the Devils went on to capture their third Stanley Cup title in a hard-fought seven game series against the upstart Mighty Ducks of Anaheim.
After playing his entire NHL career with the Devils and winning three Stanley Cups, the veteran defenseman announced his retirement from the game in the summer of 2003 and during the 2005-06 season saw his number "3" jersey retired by the club.