According to Ashkenazi custom, the Hebrew hymn “It Came to Pass at Midnight” is recited near the end of the seder. Laura Lieber analyzes this sophisticated poetic work, originally composed to be read in synagogues, and tells its author’s story:
The song . . . was not written for [the seder] night, nor is it an independent composition. Instead, it was part seven of the poem Oney fitrey raḥamatayim (The Vigor of the Openers of Wombs), composed by Yannai (late 5th–early 6th century CE), the first Hebrew poet to use end-rhyme and to sign his works with a signature acrostic.
Most of Yannai’s poems, including this one, belong to the genre known as q’dushta’ot, [singular q’dushta]. In the synagogues of the Land of Israel (up until the 7th century CE or so), the weekly Torah reading was divided up into s’darim [singular sidra], much smaller units than the Babylonian parashiyot that we use today, and the Torah was completed not yearly but roughly twice every seven years. Yannai composed a different q’dushta for each sidra, to be recited on the Shabbat when the sidra was read in synagogue.
The poem “The Vigor of the Openers of Wombs,” was composed to be recited for the sidra “And It Came to Pass at Midnight” (Exodus 12:29–51). The sidra tells the story of the death of the firstborn and Israel’s escape from Egypt, and this liturgical poem embellishes these themes, which are central to the Passover story; these affinities explain why Yannai’s poem became connected to the Passover liturgy. Indeed, because of its association with Passover, this composition ended up as Yannai’s only surviving poem until his voluminous and revelatory body of work was rediscovered in the Cairo Genizah.
Read more on theTorah.com: https://www.thetorah.com/article/it-came-to-pass-at-midnight-from-the-amidah-to-the-passover-haggadah