"I appreciate the opportunity to bid you a proper farewell," Tillerson told the group.
The former Exxon Mobil CEO said that Washington can be a "mean-spirited" town but one does not have to choose to participate in it.
Tillerson also thanked his coworkers for their hard work since the Trump administration took office in January of 2017.
Earlier this month, US President Donald Trump announced via Twitter that he fired Tillerson and nominated CIA Director Mike Pompeo to take his place. Trump told reporters later in the day that he disagreed with Tillerson on policy issues such as the Iran nuclear agreement.
Tillerson has already turned over his day-to-day responsibilities to Deputy Secretary of State John Sullivan, but his tenure will not officially end until midnight on March 31.