The series stars Georgina Sherrington and Felicity Jones (as Mildred Hubble and Ethel Hallow respectively) as well as veteran British actress Una Stubbs as the eccentric chanting teacher.

Revolving around Miss Cackle's Academy for Witches, a school for magic, The Worst Witch follows the adventures of Mildred and her friends. Mildred's clumsy personality leads the girl to disastrous situations, and she is thus considered the worst student in the whole school. The benevolent headmistress, Miss Cackle, is generally understanding, whereas Mildred's form teacher Miss Hardbroom thinks she just isn't trying hard enough. Mildred's friends include Maud Spellbody, a rotund, sensible girl who is always trying to avoid confusion, and Enid Nightshade, a practical joker who is more likely than Mildred to get them all into trouble. The three girls have a strong rivalry with Ethel Hallow, a high-born, snobbish and vindictive classmate.

Based upon the much loved books by Jill Murphy, the first season dramatised The Worst Witch and The Worst Witch Strikes Again, the second series dramatised A Bad Spell For The Worst Witch and The Worst Witch All At Sea. Both of these two series also contained original stories. The third and final series continued with purely original material. The Worst Witch aired for a total of 40 episodes.