He spent a summer as an editorial assistant for NPR in Washington D.C. From 1994 to 1999, Quintanilla served as a staff reporter for The Wall Street Journal where he wrote full-time for the newspaper's Chicago bureau, covering airlines, manufacturing and economic issues.

[2] He, along with others at CNBC were berated by Jon Stewart in the aftermath of the financial crisis of 2007–2008 for failing to predict the downturn and ask tough questions of Wall Street executives.

On his show, Quintanilla had once asked Allen Stanford, later known as the orchestrator of a "massive Ponzi scheme", how it felt to be a billionaire.

From 2010 until September 2015, Quintanilla substitute-anchored weekday and weekend editions of NBC Nightly News, covering when hosts Brian Williams and Lester Holt were on assignment or away.

[4] On October 28, 2015, Quintanilla was one of CNBC's moderators of the third of the 2016 Republican Party presidential debates and forums at the University of Colorado Boulder.