Kelly is an English-language, gender-neutral given name with strong Irish roots. It developed both as an Anglicized form of the traditional masculine name Ceallach and through the adoption of the Irish surname Ó Ceallaigh as a first name. Ó Ceallaigh literally means descendant of Ceallach. Several distinct Irish families historically bore this surname, notably powerful lineages associated with Uí Maine in parts of present-day Galway and Roscommon.

The original meaning of Ceallach is uncertain, and references offer several interpretations. Older scholarship connects it with war, strife, or contention, while other explanations suggest bright-headed. A further interpretation links it to the Irish word ceall, referring to a church or monastic cell, producing meanings such as frequenter of churches. Because specialists do not agree on a single derivation, Kelly should not be assigned one definitive literal meaning; descendant of Ceallach is the most secure etymological explanation.

Kelly illustrates the widespread English-speaking practice of turning surnames into personal names. It was used predominantly for boys before the mid-20th century, then became increasingly fashionable for girls during the 1940s and 1950s. The public prominence of actress and Princess of Monaco Grace Kelly and a female character in the television series Bachelor Father likely helped this transition. Its long use for both sexes gives Kelly a notably unisex cultural identity. Symbolically, it often evokes Irish ancestry, family continuity, and the adaptability of Gaelic names within the wider English-speaking world, although these associations are cultural rather than literal definitions.