Jack registered for the World War I draft in New Wilson, Oklahoma at the age of 24 around 1916, giving his profession as undertaker. Jack served in the United States Army from September 19, 1917 to May 6, 1919.

Jack is first mentioned in law enforcement as having served on the Jal Police Department, perhaps even being chief of police, before coming to serve as a deputy sheriff under Sheriff Bob Beverly of Lea County.

1932 saw several major arrests. On April 19, deputies Jack Seay and Don McCombs followed a tip that individuals connected to a bank robbery in O’Donnell, Texas the week before might be in Hobbs. Accompanied by federal agent George E. Lilley working out of El Paso, they approached a house in which a car fitting the description of the suspect’s vehicle was parked. As they neared the front door, it opened and gunfire erupted from inside. They backed away and called for backup as the suspects fled in their car. Shortly afterward, they stole another car from a local resident, but in so doing, were delayed long enough for the lawmen to catch up with them. One of the suspects was shot in the ensuing gunfight. The remaining suspects were later arrested in Texas.

The next day, Seay and Lilly arrested two men on charges of passing counterfeit currency in Hobbs, unrelated to the earlier case. Two months later, on June 25, 1932, Seay was ambushed and shot during the investigation of another counterfeiting case. The alleged assailant was Fritz Kilpatrick, believed to be passing counterfeit $10 bills in the area. The attack took place at a rooming house where Kilpatrick had been staying. Kilpatrick was said to have opened fire on Seay as he came to Kilpatrick’s room. Seay was seriously injured resulting in his partial paralysis and other injuries and never regained the ability to walk. Immediately after Seay’s shooting, he was taken to Lubbock where he survived the first of many surgeries.

In 1933, Kilpatrick was tried and convicted of counterfeiting and sentenced to fifteen years in prison. Seay was carried into the courtroom by four men and had testified at the trial.

Deputy Seay died in 1953 and is buried in Fairview Cemetery in Albuquerque along with his wife, Mary Little Seay, who had predeceased him in 1951. The Seays had lived in Albuquerque for a number of years. While living in Albuquerque, Jack had been a rancher and tourist court owner. He had been an active member of the Elks Lodge and the American Legion, according to his obituary.