Judge Magnis has been a lawyer for more than 30 years. He earned a Bachelor of Science degree in psychology from the University of Tulsa; where he went on to earn his law degree in 1983. He began his career in public service at Legal Services Eastern Oklahoma where ran a legal clinic for senior citizens. In 1988, he moved to Dallas to be closer to his family. He worked briefly in private practice before returning to public service in 1989 when he joined the Dallas County Public Defender’s Office.

In the Public Defender’s Office Judge Magnis began as a misdemeanor attorney representing indigent defendants in Dallas County accused of Class A and Class B misdemeanor offenses punishable by up to one year in jail. Judge Magnis mastered trial and advocacy skills quickly and within a year was promoted to felony attorney. During his time as a felony attorney Judge Magnis represented thousands of indigent defendants accused of all levels of felonies including capital murder. Judge Magnis became well known and respected in the Dallas County criminal law community as a zealous and skillful trial attorney.

In 1994 Judge Magnis was promoted to felony supervisor a position which allowed him to develop the leadership skills for which he is well known. During this time Judge Magnis supervised and mentored younger lawyers while representing a large caseload of clients. He represented thousands of clients and developed extensive trial experience, which he shared regularly with his co-workers. During his tenure Judge Magnis helped the Public Defender’s Office develop its first web site and implement its first case management system. Additionally in the late 1990s Judge Magnis served as the Public Defender’s Office's representative to the working committee that created the Dallas Divert Court. This early drug court continues to divert low level drug offenders out of the criminal justice system to this day.

In 2006 while the senior trial attorney for the Public Defender’s 0ffice Judge Magnis launched his first of three successful campaigns for district judge.