Her clients have included Russian state-owned businesses and Petr Katsyv's son, Dennis Katsyv, owner of investment firm Prevezon Holdings.  Petr is the vice president of the state-owned Russian Railways and a former deputy governor of the Moscow region. 
Veselnitskaya is known for leading opposition to the Magnitsky Act. Veselnitskaya's campaign against it included an unsuccessful attempt to get it repealed in Washington to repeal the Act and was also involved in the making of The Magnitsky Act — Behind the Scenes — an anti-Magnitsky film that premiered in June 2016. 
She provided the film crew with "the real proofs and records of testimony" according to RussiaTV5. In response to the adoption of the Magnitsky Act, the Russian government restricted American adoption of Russian children, issued a list of US officials prohibited from entering Russia, and posthumously convicted Magnitsky as guilty. The Russian government also reportedly lobbied against the act via a public relations company led by Kenneth Duberstein.