mid-15c., qualifien, transitive, "to invest with (a quality), impart a certain quality to," from French qualifier (15c.) and directly from Medieval Latin qualificare "attribute a quality to; make of a certain quality," from Latin qualis "of what sort?," correlative pronominal adjective (see quality) + combining form of facere "to make" (from PIE root *dhe- "to set, put").
Meaning "to limit, modify by a limitation or reservation, restrict" is from 1530s, as is the sense of "to have or have taken the necessary steps for rendering oneself capable of holding an office, etc." The sense of "to be or become fit for an employment, office, etc." is by 1580s. Related: Qualified; qualifying.