A canola cultivar designated NQC02CNX21 is disclosed. The invention relates to the seeds of canola cultivar NQC02CNX21, to the plants of canola NQC02CNX21, to plant parts of canola cultivar NQC02CNX21 and to methods for producing a canola plant produced by crossing canola cultivar NQC02CNX21 with itself or with another canola line. The invention also relates to methods for producing a canola plant containing in its genetic material one or more transgenes and to the transgenic canola plants and plant parts produced by those methods. This invention also relates to canola cultivars or breeding cultivars and plant parts derived from canola cultivar NQC02CNX21, to methods for producing other canola cultivars, lines or plant parts derived from canola cultivar NQC02CNX21 and to the canola plants, varieties, and their parts derived from use of those methods. The invention further relates to hybrid canola seeds, plants and plant parts produced by crossing the canola cultivar NQC02CNX21 with another canola cultivar.