[2] When he was six months old, his mother DeeDee began dating her future husband, Jeffrey Knierim, who adopted Chris.

[16] Scimeca/Knierim won the gold medal in their first ever international event, the 2012 Coupe Internationale de Nice in October.

[15] After a number of withdrawals by other teams, they received a Grand Prix assignment, the 2012 NHK Trophy in November, where they placed fourth.

They were assigned to the 2013 Four Continents Championships but withdrew just before the event when Scimeca injured her right foot in practice.

In January, they won the pewter medal at the 2014 U.S. Championships and were named second alternates to the 2014 Winter Olympic team.

Knierim had additional surgery in March to remove the metal hardware in his leg, which had been causing discomfort.

They were assigned two Grand Prix events, placing fourth at both 2014 Skate America and 2014 Trophée Éric Bompard.

At the 2015 U.S. Championships, Scimeca/Knierim captured their first national title, setting new U.S. record scores in both the short program and the free skate.

[21] Scimeca/Knierim won SKATING magazine's 2015 Readers’ Choice Skaters of the Year Award, also known as the Michelle Kwan Trophy.

[22] Scimeca/Knierim began their season at 2015 Nebelhorn Trophy where they won the silver medal behind reigning Olympic champions Tatiana Volosozhar / Maxim Trankov.

Scimeca/Knierim went on to win the bronze medal at 2015 NHK Trophy, which helped qualify them for the 2015–16 Grand Prix Final in Barcelona, where they placed seventh.

She was properly diagnosed with a rare, life-threatening gastrointestinal condition in August and underwent two abdominal surgeries that month.

[28] Alexa Knierim underwent additional surgery on November 1 and returned to training by the middle of that month.

[26] Alexa Knierim's illness involved regular episodes of vomiting, debilitating pain, difficulties with sleeping, eating or drinking, as well as significant weight loss.

In February, the Knierims made a strong return to competition at the 2017 Four Continents Championships, where they placed sixth in a deep field of Chinese and Canadian pairs.

The pair then competed at the 2017 World Championships, where they skated two strong programs and placed 10th in an exceptionally deep field.

The Knierims began their season at the 2017 U.S. International Classic, where they won the silver medal and were narrowly edged by Canadians Kirsten Moore-Towers and Michael Marinaro.

They placed 1st in the short program, 1st in the free skate, and performed a quadruple twist in competition for the first time since 2016.

They placed a strong 4th in the short program with a season's best score, defeating top pairs from China, France, and Italy.

They finished fifteenth overall after an uncharacteristically shaky skate by Alexa that included a fall on a death spiral.

[39] In early November, the Knierims won the bronze medal at their second Grand Prix event, 2018 NHK Trophy, ahead of Canadians Kirsten Moore-Towers and Michael Marinaro.

In early December, they won the silver medal at 2018 Golden Spin of Zagreb, placing 1st in the free skate and finishing one point from 1st overall.

In the short program, they had an uncharacteristic big error on their signature triple twist, typically their best element.

It was revealed after the competition that Chris Knierim had been suffering from a torn wrist ligament that requires surgery to repair.

[43] They had a strong start to their season at 2019 CS Nebelhorn Trophy where they won the silver medal with a total score of 202.41.

[44][45] At their second Grand Prix event, 2019 NHK Trophy, they placed fifth in the short program with a fall and a completely invalidated death spiral.

They skated a completely clean short program and scored 77.06, a new record at the U.S. Championships, and won that segment by nearly seven points.

[50] The Knierims were on the official entry list for the 2020 World Championships that was released on February 26, but on that same day it was announced that Chris Knierim was retiring from the sport, citing injuries and ongoing bouts of depression that had come to a head at the Four Continents Championships.