Grenell himself tweeted, "The President will announce the Nominee (not me) sometime soon."
Despite lawmakers expressing doubt that Grenell has the experience necessary to serve in the nation's top intelligence post, the White House asserted Thursday that he has "years of experience" working with the intelligence community.
"Today, the President designated United States Ambassador to Germany Richard Grenell as Acting Director of National Intelligence," White House press secretary Stephanie Grishman noted Thursday morning. "Ambassador Grenell was confirmed to his role as Ambassador by the Senate in April 2018, and he has years of experience working with our Intelligence Community in a number of additional positions, including as Special Envoy for Serbia-Kosovo Negotiations and as United States spokesman to the United Nations."
Grisham added Grenell "is committed to a non-political, non-partisan approach as head of the Intelligence Community" and President Trump "has every confidence that Ambassador Grenell will perform his new duties with distinction."
In a statement, Maguire thanked the president for the opportunity to serve in the temporary position.
"This has been the opportunity of a lifetime, and I am grateful for the tireless efforts and support of our intelligence professionals," according to the statement. "I am committed to leading the IC until Ambassador Grenell assumes the role, and look forward to the next challenge."
In his tweet, the president said Maguire may serve in another capacity within the administration.
The 53-year-old is a staunch Trump supporter who has served as ambassador in Berlin since May 8, 2018. He was confirmed by the U.S. Senate in a 56-42 vote on April 26, 2018.
Grenell will become the first openly gay member of the Cabinet. The Michigan native is also a former spokesman at the United Nations and worked on the 2012 presidential campaign of Sen. Mitt Romney, R-Utah.
Sen. Mark Warner, the ranking Democrat on the Senate Select Committee on Intelligence, criticized Trump's selection, contending the president is "flouting the clear intent of Congress when it established the Office of the Director of National Intelligence in 2004."
“The intelligence community deserves stability and an experienced individual to lead them in a time of massive national and global security challenges," Warner, D-Va., wrote in a statement. "And at a time when the integrity and independence of the Department of Justice has been called into grave question, now more than ever our country needs a Senate-confirmed intelligence director who will provide the best intelligence and analysis, regardless of whether or not it’s expedient for the President who has appointed him."
While many Republican senators remained silent about the appointment, House Speaker Nancy Pelosi also issued a statement questioning Grenell's qualifications.
"Sadly, President Trump has once again put his political interests ahead of America’s national security interests by appointing an Acting Director of National Intelligence whose sole qualification is his absolute loyalty to the President."
"Once again, the President has shown his contempt for our Constitution’s system of checks and balances by sidestepping the Senate’s constitutional authority of confirmation with the installation of another Acting official that he knows cannot be confirmed even in a Republican-controlled Senate,” she said.
The Intelligence Reform and Terrorism Prevention Act of 2004, the law which created the post, specifies that "Any individual nominated for appointment as Director of National Intelligence shall have extensive national security expertise."
According to ABC News' records, on Sept. 14, 2019, Grenell joined the president at the White House for dinner with Fred and Cindy Warmbier, whose son Otto died shortly after being released from captivity in North Korea in June 2017.
Grenell received a master's degree in Public Administration from Harvard University and completed a bachelor degree at Evangel University in Springfield, Missouri, according to his biography posted on the State Department's website.
ABC News' Luc Bruggeman, Trish Turner and Cindy Smith contributed to this report.