After interning at CBS while still in college, Harlow continued working for CBS MarketWatch and as an assistant producer for CBS Newspath after graduation. Harlow then became an anchor and reporter for NY1 News' Local Edition. While at NY1, Harlow's news beat covered Staten Island and New Jersey, including reports on local politics, the economy, and local cultural events.
In September 2007, Harlow was hired by Forbes.com Video Network, where her area of coverage expanded to fashion, entertainment and business topics.
In 2013, while reporting on the conviction of two Steubenville, Ohio, high school football players for the rape of a sixteen-year-old, Harlow stated that it was "Incredibly difficult, even for an outsider like me, to watch what happened as these two young men that had such promising futures, star football players, very good students, literally watched as they believed their lives fell apart ... when that sentence came down, [Ma'lik] collapsed in the arms of his attorney. ... He said to him, 'My life is over. No one is going to want me now.'" This apparent expression of sympathy for the rapists provoked widespread criticism.  A petition requesting that CNN apologize on the air for sympathizing with the Steubenville rapists received over 250,000 signatures within two days of CNN's report. Neither Poppy Harlow nor CNN have responded to said petition or viewer concerns, as of July 2014.