In general, the MLA follows The Chicago Manual of Style for the capitalization of professional titles (“Titles”).

Thus, we capitalize a professional title when it is used before a person’s last name (e.g., President Smith), but we lowercase the title when it is used after the name (e.g., Jane Smith, the president of Cleopatra College, spoke at the ceremony), instead of the name (e.g., The president of Cleopatra College spoke at the ceremony), or as an adjective before the name (e.g., The Persian king Darius I oversaw the construction). In some materials, such as programs and invitations, we sometimes make an exception and capitalize a professional title when it is used as an adjective before the name (e.g., Cleopatra College President Jane Smith). 

When you are styling professional titles, we recommend that you strive for consistency and keep a style sheet that lists any exceptions.

Work Cited

“Titles and Offices—the General Rule.” The Chicago Manual of Style, 17th ed., sec. 8.19, U of Chicago P, 2017, www.chicagomanualofstyle.org/book/ed17/
part2/ch08/psec019.html.