In 1975, after serving as a psychiatrist for the Canadian Forces, he started working with assault offenders and participated in numerous trials as an expert witness in the psychiatric domain.

Mailloux served as an on-air psychiatrist for the Quebec version of the reality show Loft Story, where he made remarks that upset the parents of a participant while analyzing her behaviour.

On September 25, 2005, he appeared on the widely viewed Québec television talk show, Tout le monde en parle and cited unspecified studies allegedly used at the Université de Montréal in psycho-education classes, stating that Black people in the Americas and Native Americans have a lower IQ average than white and Asian Americans, a currently controversial topic of study about race and intelligence.

Mailloux was indefinitely barred from the Collège des médecins in January 2007 for prescribing abusive doses of neuroleptics to two of his patients and because of his earlier radio and TV claims and comments.

However, the CKRS radio station and a viewer circulated a petition for the Collège to reinstate Mailloux until his hearing in front of the discipline committee.

On March 20, 2007, a Journal de Montréal news article reported that in an interview with Télé-Québec's host Richard Martineau, Mailloux said that women manage stress more poorly than men, that they are also less able to make decisions under pressure.

[11] In September 2007, during an interview on a Rouyn-Noranda radio station, Mailloux made controversial comments about the mayor of Saguenay, Jean Tremblay, after he read a memoir at the Bouchard-Taylor Commission on the reasonable accommodation.

Mailloux also criticized the people of the city, saying its citizens lacked judgement by voting for Tremblay, also explaining the high unemployment rate in the Saguenay-Lac-Saint-Jean region.