beginning in 1897, mcnary taught the law to his younger brother charles l. mcnary in salem. charles passed the bar in 1898 and joined his brother in practicing law in salem. mcnary was in private practice from 1898 until 1913. during this time, he served as deputy district attorney for marion county between 1898 and 1904, and in 1905 became the district attorney for oregon’s third judicial district. while in office he helped to prosecute some of those involved in the oregon land fraud scandal. when mcnary was the district attorney, his brother worked under him as an assistant district attorney. in 1912, he taught at the willamette university college of law as a professor of corporations under his brother who was the dean.