Best is known for prolific filing of Freedom of Information Act (FOIA) requests on behalf of MuckRock and co-founding the whistleblower site Distributed Denial of Secrets (DDoSecrets).

[7][8][9] Best has said that before becoming a transparency activist and investigative journalist, they worked for Wikistrat[10] and subcontractors hired by the Intelligence Community before becoming disillusioned.

[9] They left over concerns for source safety and bureaucratic obstruction,[9] and have discussed disillusionment about surveillance, police militarization, and expansion of the military.

With the help of national security attorneys Mark Zaid and Brad Moss, the ban was lifted after several months and their requests were reopened.

[29] On 19 July 2016, in response to the Turkish government's purges that followed the coup attempt,[30] WikiLeaks released 294,548 emails from Turkey's ruling Justice and Development party (AKP).

Assange urged Best to decline, intimating that he was in contact with the persona's handlers, and that the material would have greater impact if he released it first.

[29] In April 2019, they revealed that Chelsea Manning's FBI files were central to the ongoing proceedings against Assange before the indictment was unsealed.

[23] According to Best, The Architect, whom they already knew, approached them and expressed their desire to see a new platform for leaked and hacked materials, along with other relevant datasets.

[41][42] In July 2020, three agents who identified themselves as part of Homeland Security Investigations visited a woman in Boston to question her about BlueLeaks, Distributed Denial of Secrets and Emma Best.

They said “it’s impossible to walk through the world and not be keenly aware of its absence.” Best added that "queer people are attracted to transparency because we’re forced into closets and into confronting broken and abusive systems"[46] In 2022, Best said "I don’t long for any nationality.

[48] After Best published private WikiLeaks chats in 2018, Julian Assange’s personal Twitter account cited their transgender status and dismissed them as a disgruntled activist.

[50] After the publication of "GabLeaks" in 2021, Gab CEO Andrew Torba released a statement in which he referred to the leakers as "mentally ill tranny demon hackers".

"[23] After Barrett "Brown's life spiraled" in 2021, he accused Best and other members of DDoSecrets of faking being transgender to obscure their histories in the intelligence community.