Cahaly was born in Georgia and grew up in Pendleton, South Carolina and received a B.A. in political science from the University of South Carolina in 1995. Cahaly is of Syrian heritage and is an Eastern Orthodox Christian. Starting as a child, he volunteered on various political campaigns, before eventually founding his own political consulting firm in 1997.
Cahaly has worked on campaigns for various Republicans, including governors Carroll Campbell, David Beasley, Mike Huckabee, Nikki Haley, Chris Christie, and Henry McMaster; US Senators Strom Thurmond, Bob Dole, Tim Scott, and Ben Sasse; and Presidents George H. W. Bush, George W. Bush, and Donald J. Trump."[better source needed]
On November 3, 2010, Cahaly was arrested by the State Law Enforcement Division (SLED) and charged with making illegal robocalls.  Cahaly denied any wrongdoing, stating "It is sad and disappointing that in this charged election cycle full of last minute surprise attacks that Democrat Incumbents and power brokers are leveraging all of their influence to create a last minute salacious headline. We are apparently today's target." The charges were subsequently dismissed in October 2012. After the charges were dropped, Cahaly filed suit against SLED officials, claiming his constitutional right to free speech had been violated. The subsequent decision of Cahaly v. LaRosa found the anti-robocall statute was a content-based restriction on speech and therefore unconstitutional, which defended the right of Cahaly to make robocalls.
Cahaly gained media attention in 2016 for being one of the few pollsters to accurately predict that Donald Trump would carry the states of Michigan and Pennsylvania in the 2016 United States presidential election. Cahaly attributed this partially on the premise of "Shy Trump Voter Theory," which claims that poll respondents are afraid to reveal that they are voting for Trump due to a "social desirability bias."
In November 2020, Cahaly appeared on Hannity on Fox News and claimed Trump would win Pennsylvania but opponents would "steal" victory from him through voter fraud: "He better win by 4 or 5% to make sure he gets victory there. That is the margin he needs to avoid what they will systematically do."
- "GOP consultant arrested for illegal "robocalls" Nov. 2, 2010 https://www.wistv.com/story/13429729/gop-consultant-to-face-sled-arrest-for-illegal-robocalls/
- Ancestry.com Collections 
- "GOP consultant arrested for illegal "robocalls"". Retrieved Oct 27, 2015.
- "Charges Against GOP Consultant Cahaly Dropped". Retrieved Oct 27, 2015.
- "Fed Court rules law Cahaly charged under unconstitutional". Retrieved Oct 27, 2015.
- "An Evaluation of 2016 Election Polls in the U.S. - AAPOR". www.aapor.org. Retrieved 2020-11-03.
- Ed Kilgore, "There’s Still No Evidence Trump Voters Are Particularly ‘Shy’" New York Magazine, JULY 29, 2020 https://nymag.com/intelligencer/2020/07/theres-still-no-evidence-trump-voters-are-particularly-shy.html
- "Four Problems With 2016 Trump Polling That Could Play Out Again in 2020," New York Times, Nov. 25, 2019
- Hall, Colby. "Trafalgar Pollster Robert Cahaly Makes Baseless Claim: Trump Will Win Pennsylvania, But 'They' Will Steal It With Voter Fraud". mediaite.com. Mediaite. Retrieved 2 November 2020.