She worked as a theatrical producer for productions which included The Potsdam Quartet and A. R. Gurney's The Middle Ages and served on the New York Theatre Workshop's board of directors.

She graduated from The Park School of Buffalo, which she later served on its board of trustees, and from Harvard University, attending Radcliffe College, with a Bachelor of Arts degree in 1977.

Clarkson announced her campaign for a seat in the Vermont Senate on April 25, 2016, at a rally attended by Rebecca White, Gabrielle Lucke, and Ernie Shand.

She won the Democratic nomination alongside Alice Nitka and Richard McCormack despite Campbell having endorsed Conor Kennedy in the primary and she placed first out of seven candidates in the general election.

[31][32] The Democratic caucus voted unanimously in 2020, to have Clarkson succeed Becca Balint as the Majority Leader after Senator Brian Campion dropped out of contention.

[38] Clarkson and Senator McCormack sponsored legislation in 2017, which created a day in honor of abolitionist John Brown, following the white supremacist Unite the Right rally in Charlottesville, Virginia.