[1] Plekanec played junior ice hockey in his native Czech Republic with the HC Kladno organization.

Assigned to the club's minor league affiliate, the Hamilton Bulldogs of the AHL, he recorded 46 points over 77 games.

Due to the 2004–05 NHL lockout, Plekanec remained in Hamilton for a third AHL season and recorded 64 points over 80 games.

Plekanec received a two-game suspension on 12 February 2009, for a slewfoot on Edmonton Oilers defenceman Denis Grebeshkov during a game the previous day.

[4] On 15 September 2014, Plekanec was named an alternate captain of the Canadiens, along with P. K. Subban, Max Pacioretty and Andrei Markov.

[5] On 16 October 2015, Plekanec and the Canadiens agreed to a two-year, $12 million contract extension, signing him through until the end of the 2017–18 season.

The following day, Plekanec (in the final year of his contract), was traded to the Toronto Maple Leafs, along with minor league player Kyle Baun in exchange for Kerby Rychel, Rinat Valiev and a second-round pick in 2018.

[7] During the opening round of the playoffs against the Boston Bruins, following a three-game suspension to Nazem Kadri, Plekanec was placed on a line with Patrick Marleau and Mitch Marner.

After his first NHL season, Plekanec competed in the 2006 World Championships, where the Czech Republic captured a silver medal in Latvia.

[20] Plekanec was granted the right to take his Canadian-born sons Matyáš and Adam to the Czech Republic rather than stay in Montreal as Vondráčková requested.

[21][22][23] Plekanec has been in a relationship with professional tennis player Lucie Šafářová since August 2018,[24] and on 4 July 2019, Safarova announced on her Instagram account that they are expecting their first child.