[6] In 2000 he graduated from the Institute of Business Administration, Academy of National Economy under the Government of the Russian Federation, faculty of "Strategic Management".

[10] Since the 2022 Russian invasion of Ukraine, he has gained a following on YouTube, hosting daily discussions with Ukrainian presidential advisor Oleksii Arestovych on his channel.

[11] In 2024 he was convicted in absentia for 11 years of corrective colony for "dissemination of knowingly false information about the Russian Army <...> motivated by political hatred".

[12] In 2012, Feygin served as one of three lawyers for Pussy Riot, a punk band arrested for an unauthorized performance in Moscow's Cathedral of Christ the Savior.

[17][18] On 19 November, Feygin and the two other lawyers for Pussy Riot withdrew from the case prior to Tolokonnikova's appeal, stating that they felt the court would be more likely to grant it if they were no longer a part of the defense.

[22] Feygin also defended Leonid Razvozzhayev, an opposition political aide who accused Russian authorities of having kidnapped him from Kyiv, Ukraine to face terrorism charges.