In a letter she sent to department employees, Solis said she decided to resign and "begin a new future" after mulling it over during the holidays and discussing it with family and friends. The 55-year-old former California congresswoman said she decided to "return to the people and places I love and that have inspired and shaped my life."
"This afternoon, I submitted my resignation to President Obama," she said. "Growing up in a large Mexican-American family in La Puente, Calif., I never imagined that I would have the opportunity to serve in a president's Cabinet, let alone in the service of such an incredible leader.
"Because President Obama took very bold action, millions of Americans are back to work. There is still much to do, but we are well on the road to recovery, and middle class Americans know the president is on their side," she said.
"Leaving the department is one of the most difficult decisions I have ever made, because I have taken our mission to heart," she said. "As the daughter of parents who worked in factories, paid their union dues and achieved their goal of a middle class life, and as the first Latina to head a major federal agency, it has been an incredible honor to serve."
In a statement released by his press secretary's office, President Obama called Solis "a tireless champion for working families."
"Over the last four years, Secretary Solis has been a critical member of my economic team as we have worked to recover from the worst economic downturn since the Great Depression and strengthen the economy for the middle class," Obama said. "Her efforts have helped train workers for the jobs of the future, protect workers' health and safety and put millions of Americans back to work.
"I am grateful to Secretary Solis for her steadfast commitment and service not only to the administration, but on behalf of the American people. I wish her all the best in her future endeavors."
Neither she nor the president made mention of what Solis' future plans may include.
She is one of several high-level officials, including Defense Secretary Leon Panetta, Secretary of State Hillary Clinton and Treasury Secretary Timothy Geithner, leaving the administration as Obama begins his second term.
In her lengthy letter, Solis outlined the "extraordinary things" the department achieved under her direction and said she is "humbled by the commitment of every single employee of this department -- from the folks here in Washington to those who directly touch communities out in the field."
"We have much to be proud of," she said.