Markus, a Fellow of the American Law Institute (ALI), served as a decorated federal prosecutor in Chicago, Section Chief with the U.S. State Department-Balkans, law clerk with the Federal Court of Appeals and district court, and law professor at, among other institutions, Oxford University (where he also earned his PhD in law), and the University of Chicago. The author of nine books and over 100 articles, Markus is a regular speaker and guest-lecturer at institutions such as Harvard Law School, Yale Law School, the Vatican, the World Bank, Georgetown Law School, the New York Mayor's Office, and the University of Chicago Law School. He stands alone as the only person to have received the US State Department's highest general service award (the Superior Honor Award) and the US Department of Justice's highest trial distinction (the Attorney General's Award).

During his time in public service, Markus and his team prosecuted "Operation Family Secrets," which National Public Radio lauded as "one of the most important criminal investigations . . . in American history" (the 1995 movie "Casino" was based on the charged criminal activities). At the time of his departure from the Department of Justice, the Chicago Sun-Times described Markus as a "street-smart prosecutor with an Oxford pedigree." His cases and legal analysis (including on issues relating to trafficking and supply chain compliance), moreover, have been featured by outlets such as The Atlantic, BBC, Bloomberg, CNBC, CNN, The Economist, The History Channel, Huffington Post, Investor's Business Daily, London Times, Los Angeles Times, MSNBC, The National Law Journal, National Geographic TV, The New York Times, Politico, Reuters, Salon, The Wall Street Journal, and The Washington Post. He is also the primary host of the White Collar Briefly podcast.  

In 2010, he founded Perkins Coie's Supply Chain Compliance Practice, the first such specialized practice among the 100 biggest law firms in the U.S.  In 2016, Markus and US District Judge Virginia Kendall co-authored the second edition of their book Child Exploitation and Trafficking: Examining Global Enforcement and Supply Chain Challenges and U.S. Responses Second Edition (Rowman Littlefield).