Hope Hicks, 29, is leaving the White House after serving Trump for three years in various capacities. This included being his campaign spokesperson and Director of Strategic Communication when Trump was sworn in as the president on January 20, 2017.
"There are no words to adequately express my gratitude to President Trump,"Hicks said in a statement.
"I wish the President and his administration the very best as he continues to lead our country," she said.
She during her testimony had told the panel that in her job, she had occasionally been required to tell white lies but had never lied about anything connected to the investigation into Russia's interference in the election.
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Trump praised Hicks for her outstanding work.
"She is as smart and thoughtful as they come, a truly great person. I will miss having her by my side but when she approached me about pursuing other opportunities, I totally understood. I am sure we will work together again in the future."
"Her departure is to be determined but it will be sometime in the next few weeks," it said.
Hicks is Trump's longest serving aide, having worked with him before he announced his candidacy.
After three years, she approached Trump and told him she wanted to leave so she could start exploring opportunities outside of the White House.
Hicks, a former model, had no political experience when she joined Trump's tumultuous campaign for the White House.
Hicks initially served as a press secretary within the White House, before taking on the role of communications director following a series of high-profile departures last year.
The White House said Hicks is a "valued adviser and counselor to the president and other senior administration officials".
Although Hicks maintained an unusually low profile over the past three years, she recently attracted scrutiny after special counsel Robert Mueller escalated his investigation into potential collusion between the Trump campaign and Russia.
Hicks' proximity to the president, and presence on his campaign from its infancy, placed her in the spotlight as a potentially key witness to the FBI's inquiry.
Hicks's first association with the Trump family was working with Trump's eldest daughter, Ivanka, on her personal apparel and licensing brand about six years ago.
"Hope Hicks is loved & admired by all who know her. Its with a heavy heart, but tremendous gratitude, that I wish her well in her next steps," Ivanka tweeted.
Hicks's departure will coincide with those of other people who have been close to the Trump family members in the White House.
Their absence will deprive Trump and his daughter and son-in-law of many of the aides who served as crucial buffers and sounding boards as a turbulent and politically uncertain year begins, The New York Times reported.
Sanders said Hicks would leave behind a void which nobody can fill.
In a little over 13 months of this administration, Hicks is the fourth individual to resign as the White House Director of Communications. The other three being Sean Spicer, Mike Dubke and Anthony Scaramucci.