Prall was born near Ringoes in East Amwell Township, New Jersey. He attended Harvard University (1906) and New York University School of Law (LL.B. 1908). After almost two decades of practicing law, Prall was elected to the legislature, first to the Assembly (1927–28), then to the State Senate (1928–36), serving as president of that body in his last two years of tenure. After the resignation of Governor A. Harry Moore, Prall served as Acting Governor for a brief period (January 3, 1935 – January 15, 1935). After completing his last term as a Senator, Prall became a judge on the Court of Common Pleas.
^Staff. "Horace G. Prall", The New York Times, April 24, 1951. Accessed May 29, 2013. "Trenton, April 23 – Horace G. Prall of Lambertville, former State Senator and Judge of Hunterdon County, died in a hospital here today of a heart attack."