[1] Following his graduation, Rothermel clerked in the law office of James T. Mitchell, a prominent Philadelphia attorney who would later serve on the Supreme Court of Pennsylvania.
In 1898, Rothermel ran for District Attorney of Philadelphia as a Republican and was elected, defeating James M.
[2] The following year, Rothermel served as prosecutor in the corruption trial of Senator Matthew Quay.
[3] After his term as District Attorney ended in 1901, Rothermel was refused renomination by the Republican machine politicians, owing to his prosecution of Quay.
He was nominated by a group of reformers on a fusion ticket, but failed to be re-elected, losing to future mayor John Weaver.