Pence, who will be joined by Secretary of State Rex Tillerson, is expected to speak around noon at the Conference on Prosperity and Security in Central America - an event taking place on the campus of Florida International University.
Vice President Mike Pence has retained outside counsel to help him navigate the ongoing probe into Russian interference in the 2016 election, according to the Washington Post, ABC News and others.
Pence's announcement comes after several weeks of deliberations, featuring several candidates, an administration official said, adding that no taxpayer money will be used.
Pence hired outside counsel to represent him before congressional inquiries and federal investigation headed by Special Counsel Robert Mueller.
A final decision was made to hire Cullen earlier this week.
Cullen previously served as Virginia attorney general and US attorney for the Eastern District of Virginia.
Cullen is no stranger to high-profile federal investigations. The law firm referred questions back to the vice president's office.
The Washington Post was first to report the news. He lashed out on Twitter Thursday, writing, "You are witnessing the single greatest WITCH HUNT in American political history - led by some very bad and conflicted people!"
Scrutiny of the president's actions has intensified since he fired Federal Bureau of Investigation director James Comey last month. As head of the Trump campaign's transition committee, he was involved in the hiring of Michael Flynn as national security adviser.