Prior to joining the NHL, Višňovský played with HC Slovan Bratislava. He was drafted 118th overall in the 2000 NHL Entry Draft by the Los Angeles Kings as their fourth choice. He made the team for the 2000–01 season and was named to the NHL All-Rookie Team after a 39-point campaign, tops among rookie defencemen. Višňovský remained with the Kings for seven seasons, recording a career-high 67 points in 2005–06. He returned to play in his home country for the locked out 2004–05 season.

On 29 June 2008, Višňovský was traded to the Edmonton Oilers in exchange for forward Jarret Stoll and defenceman Matt Greene, on the day before his no trade clause would take effect. He was put on the injured reserve on 5 February 2009, after dislocating his shoulder in a game against the Chicago Blackhawks on 3 February. It was later revealed Višňovský required season-ending surgery to repair his labrum.

On 3 March 2010, Višňovský was traded to the Anaheim Ducks for Ryan Whitney and a sixth round pick in the 2010 NHL Entry Draft. On 4 March 2011, Višňovský scored the first hat trick by a defenseman in Anaheim Ducks history, the third goal coming with four seconds left in overtime.

On 22 June 2012, Višňovský was traded to the New York Islanders for a second round pick in the 2013 NHL Entry Draft. Shortly thereafter, Višňovský filed a grievance through the National Hockey League Players’ Association (NHLPA) seeking to void the trade, claiming that the no trade clause in his original contract with Los Angeles was still valid, since he never revoked it when Edmonton traded him to Anaheim. An arbitrator ruled against Višňovský in this case and the trade was upheld.

The Islanders suspended Višňovský because he did not report to the team for the start of the NHL season. His agent, Neil Sheehy, said on 26 January 2013, that Višňovský will report to the team by 11 February. Višňovský later signed a two-year extension with the Islanders worth $4.75 million per year.

After parts of three seasons with the Islanders, Višňovský left as a free agent and was un-signed over the summer. On 16 September 2015, he was signed to a try-out contract to attend the reigning Champions in the Chicago Blackhawks, training camp. Upon his release at the conclusion of training camp by the Hawks, Višňovský returned to Bratislava midway into the 2015–16 season, signing a one-year deal on 27 October 2015. He played his last professional game in November 2016.