During law school at the University of Texas, he served as Intern to the Honorable Justice John Cornyn, Supreme Court of Texas, in 1995. He also had the honor of serving as an intern to the late Professor Charles Alan Wright, who was considered to be the foremost authority in the United States on Constitutional law and federal procedure and was the coauthor of the 54-volume treatise, Federal Practice and Procedure with Arthur Miller.

Frank was a member of the ATLA Mock Trial Regional Champion, State Finalist, and National Quarter-Finalist Teams in 1995 and 1996. He was subsequently inducted as a National Member of The Order of Barristers.

After graduating from law school, Mr. Guerra joined the law firm of Allen, Stein, Powers, Durbin & Hunnicutt, where he practiced insurance defense and civil litigation law. He managed the Rio Grande Valley Office of that firm from 1999 to 2001 and spent his time trying lawsuits every week in front of South Texas juries. One of the first cases he tried was a double death case against Mikal Watts in Webb County, Texas. After the hard fought battle, they forged a friendship that would last forever. Frank eventually joined the San Antonio office of Harris & Watts (a predecessor firm to Watts Guerra LLP) in 2001.