She worked at a variety of financial firms, including Citibank, Capital One, Chase Manhattan Bank, and American Express, from 1996 to 2008[2] and operated her own consulting business, Karen Lewis Market Research, from 2004 to 2006.

[3] In May 2009, Lewis Young announced that she would run for a seat on the Frederick Board of Aldermen, motivated by the 2008 United States presidential election and her community involvement.

[2] In June 2021, Lewis Young announced that she would run for Maryland Senate in 2022, seeking to succeed her husband, Ronald,[16] who later endorsed her campaign.

[9] In December 2015, Lewis Young said she disagreed with Governor Larry Hogan's decision to withhold funding from Maryland's costliest public school systems.

[22] During the 2017 legislative session, Lewis Young supported a bill to give the student member of the Frederick County Board of Education partial voting rights.

[33] During the 2016 legislative session, Lewis Young introduced a "right to try" bill that would allow terminally ill patients to try medication approved by the Food and Drug Administration but not available to the general public.

[39] In March 2019, Lewis Young voted for the End-of-Life Option Act, which would have provided palliative care to terminally ill adults.

[42] In November 2015, Lewis Young said she supported using an independent redistricting commission to draw Maryland's congressional districts, but said she preferred a "national solution" to gerrymandering.

[48] In 2017, Lewis Young introduced a bill requiring the Maryland State Police to create a statewide sexual assault tracking system.

[49] In January 2019, Lewis Young was one of nine Maryland lawmakers to add their names to a manifesto signed by 326 state legislators to reaffirm their commitment to protecting abortion rights.