Having won the Junior Fed Cup in 2014, Kenin was nominated for her first senior Fed Cup tie in the 2018 final against the Czech Republic.
Both teams were missing their best players, with the Williams sisters, Sloane Stephens, and Madison Keys for the United States, as well as Plíšková and Petra Kvitová for the Czech Republic all unavailable.
Kenin and Alison Riske were selected to play singles against Barbora Strýcová and Kateřina Siniaková.
Kenin lost both of her singles matches in three sets, as the Czech Republic swept the tie 3–0 to win the Fed Cup.
The decisive third rubber between Kenin and Siniaková was particularly close.
The match lasted three hours and forty-five minutes and ended with Siniaková needing to save two match points on Kenin's serve in the third set before coming from behind to win.

Kenin represented the United States again in 2019.
In the first round against Australia, she lost her only match to Ashleigh Barty, who won both of her singles rubbers as well as the decisive doubles rubber to lead Australia to a 3–2 victory.
The United States' next tie was against Switzerland as part of the World Group Play-offs.
After Keys lost the first match and Stephens won both of her singles rubbers, Kenin was selected to play the last singles rubber against Timea Bacsinszky.
Kenin defeated Bacsinszky to win the tie 3–1 and keep the United States in the World Group for 2020.

A week after winning the 2020 Australian Open, Kenin represented the United States in the Fed Cup Qualifying Round.
She defeated Anastasija Sevastova in the opening match of  the rubber against Latvia.
The following day she lost to Jeļena Ostapenko while Serena Williams lost to Sevastova.
This forced a fifth and decisive doubles rubber match between Kenin/Bethanie Mattek-Sands, and Ostapenko/Sevastova.
The American duo won in two sets in only 75 minutes to send the United States to the Fed Cup Finals.
Having won the Junior Fed Cup in 2014, Kenin was nominated for her first senior Fed Cup tie in the 2018 final against the Czech Republic. Both teams were missing their best players, with the Williams sisters, Sloane Stephens, and Madison Keys for the United States, as well as Plíšková and Petra Kvitová for the Czech Republic all unavailable. Kenin and Alison Riske were selected to play singles against Barbora Strýcová and Kateřina Siniaková. Kenin lost both of her singles matches in three sets, as the Czech Republic swept the tie 3–0 to win the Fed Cup. The decisive third rubber between Kenin and Siniaková was particularly close. The match lasted three hours and forty-five minutes and ended with Siniaková needing to save two match points on Kenin's serve in the third set before coming from behind to win.
Kenin represented the United States again in 2019. In the first round against Australia, she lost her only match to Ashleigh Barty, who won both of her singles rubbers as well as the decisive doubles rubber to lead Australia to a 3–2 victory. The United States' next tie was against Switzerland as part of the World Group Play-offs. After Keys lost the first match and Stephens won both of her singles rubbers, Kenin was selected to play the last singles rubber against Timea Bacsinszky. Kenin defeated Bacsinszky to win the tie 3–1 and keep the United States in the World Group for 2020.
A week after winning the 2020 Australian Open, Kenin represented the United States in the Fed Cup Qualifying Round. She defeated Anastasija Sevastova in the opening match of  the rubber against Latvia. The following day she lost to Jeļena Ostapenko while Serena Williams lost to Sevastova. This forced a fifth and decisive doubles rubber match between Kenin/Bethanie Mattek-Sands, and Ostapenko/Sevastova. The American duo won in two sets in only 75 minutes to send the United States to the Fed Cup Finals.
Sofia Kenin