Day's first job after high school was performing on the Louisiana Hayride as a sideman accompanying developing country artists including Hank Williams, Webb Pierce, Willie Nelson, Jim Reeves, Ray Price and Elvis Presley.

[4] Just after high school graduation in 1951,[3][6] he auditioned for and was granted a job in the house band on the "Louisiana Hayride", a popular country music radio show which at the time rivaled Nashville's Grand Ole Opry.

[7] On the radio broadcast, Day gained experience in backing performers who were on their way to becoming megastars, including Hank Williams, Faron Young, Johnny Horton, Jim Reeves and Elvis Presley .

[3] Day moved to Nashville in 1955 and became a session player, performing on classic hits such as "Crazy Arms" and "Heartaches by the Number" (Ray Price)[6] and "Pick Me Up on Your Way Down"(Charlie Walker).

[9] After about six months, Day left Nelson to perform with various artists including Ferlin Husky, Buddy Emmons, and Little Jimmy Dickens.

[3] In the late 1950s, Day formed a business partnership with Buddy Emmons and Shot Jackson in the Sho-Bud Company.

[13] In the 1970s, Day left Nashville to move to Texas to live in Buda, a commuter town south of Austin.

He became active in the Texas music scene, working with Price, Nelson and Johnny Bush; he ventured back to Nashville only occasionally.

[9] According to former bandmate Johnny Bush in his 2017 book, Whiskey River (Take My Mind): The True Story of Texas Honky-Tonk, Day was a "first-call" session player and the "master of the E9 sound" on country ballads, but had issues with substance abuse which allowed Pete Drake to take over Day's session work.

[14]: 119  In the book, Bush said Day quit drinking in the last twenty years before he died, but his health had suffered because of it.