[1][2] Southworth was born in Little Cooley, Pennsylvania, graduated in 1914 with a physics degree from Grove City College, and studied one year at Columbia University.

In June 1917 he joined the National Bureau of Standards, then in 1918 moved to Yale University to teach in a Signal Corps school.

He remained at Yale to complete a doctorate in 1923 on the measurement of the dielectric constant of water at frequencies above 15 MHz.

Southworth left Yale for a position with the American Telephone and Telegraph Company, where he first helped edit the Bell System Technical Journal, but then switched to researching shortwave radio propagation.

After he constructed a 5-in.-diameter waveguide with a length of 875 feet, the project was moved to the Bell Telephone Laboratories in Holmdel, New Jersey, where he spent the rest of his career until retirement in 1955.