[2] Marquis was appointed District Attorney in Clatsop County by then-Governor Barbara Roberts after his predecessor was convicted and disbarred for gross prosecutorial misconduct.

In 2019 Marquis was appointed Director of Legal Affairs and Enforcement of Animal Wellness Action, a Washington, D.C.–based anti-cruelty organization headed by Wayne Pacelle, former CEO of the Humane Society of the United States.

[7] Marquis worked as a reporter for the Los Angeles Daily Journal in the early 1980s and the speechwriter to California Attorney General John Van de Kamp in the mid-1980s.

In October 2011 Marquis was one of four panelists invited to discuss capital punishment at the New Yorker Festival on a panel that also included Innocence Project founder Barry Scheck, death penalty opponent Danalynn Recer, and crime victim's advocate Marc Klaas.

[3] Marquis was a member of the Board of Directors of the National District Attorneys Association from 1997 until his appointment as a Circuit Judge Pro Tem in 2019.