Rundblad scored his first Elitserien goal on March 14, 2009, in a playoff game against Linköpings HC. NHL Central Scouting ranked Rundblad sixth among European skaters for the 2009 NHL Entry Draft, one spot behind Skellefteå AIK teammate Tim Erixon. The following season, Rundblad remained with Skellefteå and scored his first regular season goal on January 30, 2010 against Mattias Modig of Luleå HF, a goal that ended up being the game-winner. On June 10, 2010, it was announced that Rundblad had signed an entry-level contract with St. Louis. On June 25, 2010, he was acquired by the Ottawa Senators in exchange for the 16th overall pick in 2010, which the Blues used to select Vladimir Tarasenko. Rundblad finished the 2010–11 season with 50 points in 55 games, the second highest point total of any defenceman in Elitserien history, after David Petrasek, who had 53 points in 2009–10. Rundblad attended his first Senators camp in 2011, and remained on the roster into the season. Rundblad made his NHL debut on October 11, 2011, against the Minnesota Wild. Rundblad's first NHL point was an assist on a goal by Peter Regin on October 15 in a game against the Washington Capitals. His first NHL goal came on November 27, 2011, against Cam Ward of the Carolina Hurricanes. On December 17, 2011, Rundblad was traded to the Phoenix Coyotes for forward Kyle Turris. Rundblad participated in the AHL All-Star Classic in Providence, Rhode Island, on January 28, 2013. He scored six goals and had 17 assists for 23 points in 32 games before the break. On March 4, 2014, Rundblad was traded to the Chicago Blackhawks in exchange for a second-round pick in 2014. In the 2015–16 season, Rundblad made the Blackhawks opening night roster primarily as the team's reserve defenseman. He provided two assists in nine games before he was placed on waivers and later reassigned to the Rockford IceHogs. Before playing with Rockford, on January 3, 2016, it was announced that Rundblad was loaned to the ZSC Lions of Switzerland's National League A for the remainder of the season. He later returned to the Blackhawks for their post-season run, appearing in three games. On July 1, 2016, Rundblad became a free agent after he was placed on waivers and bought-out from the remaining year of his contract with the Blackhawks. He signed to return to the ZSC Lions of the Swiss top-flight National League A on September 2, 2016. After finishing his ZSC stint, he made the jump to the KHL, signing with SKA Saint Petersburg on May 10, 2017.
