Gillibrand's tenure at Davis Polk included serving as a defense attorney for tobacco company Philip Morris during major litigation, including both civil lawsuits and U.S. Justice Department criminal and civil racketeering and perjury probes. As a junior associate in the mid-1990s, Gillibrand defended the company's executives against a criminal investigation into whether they had committed perjury in their testimony before Congress when they claimed that they had no knowledge of a connection between tobacco smoking and cancer. Gillibrand worked closely on the case and became a key part of the defense team. As part of her work, she traveled to the company's laboratory in Germany, where she interviewed scientists about the company's alleged research into the connection. The inquiry was dropped and it was during this time that she became a senior associate.