He has previously played for the Boston Bruins, Minnesota Wild, Florida Panthers, and New York Rangers of the NHL and Ak Bars Kazan of the KHL.

[13] Kampfer's high average ice time during his first 17 games as a Bruin, combined with the confidence shown by the coach in power play and key defensive situations, were intended to help make his case for a more permanent position on the roster, as when defenseman Mark Stuart was traded to the Atlanta Thrashers on February 18, 2011, center Rich Peverley was acquired in return, and Kampfer's continued presence with the Bruins proved valuable.

His speed and ability to jump into the play, as recommended by the coaching staff, added a much-needed element to the Boston Bruins as of January 13, 2011.

[18] Kampfer missed the opening games of the 2011–12 NHL season due to a knee injury to the other leg suffered during training camp.

[23] Kampfer spent the majority of the 2013–14 season with Minnesota's new AHL affiliate, the Iowa Wild, playing in 69 games, scoring six goals and 26 points.

[27] However, on October 6, 2014, Kampfer and Andrew Yogan were traded by the Rangers to the Florida Panthers in return for Joey Crabb in order to open a roster spot for Anthony Duclair.

After clearing, Kampfer was subsequently dealt back to the Rangers on November 8, 2016, along with a conditional seventh-round pick in the 2018, in exchange for Dylan McIlrath.

[32] The same day, the Rangers acquired defenseman Brendan Smith from the Detroit Red Wings[33] and Kampfer was returned to Hartford on March 1.

[40] Following his 11th professional season, Kampfer left the NHL as a free agent and signed his first contract abroad in agreeing to a one-year deal with Russian-based Ak Bars Kazan of the Kontinental Hockey League (KHL) on July 5, 2021.

As a free agent following Ak Bars playoff exit, Kampfer returned to North America and agreed to a one-year, two-way contract with the Detroit Red Wings on May 23, 2022.

He made 44 appearances on the blueline for the Griffins, posting 4 goals and 22 points before he was traded by the Red Wings to the Arizona Coyotes in exchange for future considerations on March 9, 2023.

[44] Following two seasons, Kampfer returned to Russia as a free agent, securing a one-year contract with Traktor Chelyabinsk on August 5, 2024.

[47] On January 13, 2022, Kampfer was named to the United States men's national team to compete at the 2022 Winter Olympics as an assistant captain.