The book received wide praise from critics, both for its emotional depth and the author's artistic decision to mix watercolor, gouache, and ink in her paintings, as well as for her usage of pastel tones against a more muted background.

Love began writing Julián Is a Mermaid while working as an actress on a Jez Butterworth play in 2014.

The book's draft, which was originally 45 pages, called "insanely long" by Love's agent, was sent to Candlewick Press, and later accepted for publishing.

[3] The 1990 documentary Paris Is Burning, which tells the story of drag queens rejected by their families who found acceptance in a different place, was another inspiration.

Love said in an interview with The Guardian that she wanted to write a story "about what [the drag queens'] lives would have been like if they'd received the kind of support from their birth families.

Sarah Hunter, writing for Booklist, praised Love's use of muted backgrounds, which helped highlight the main scenes, as well as her "saturated, opaque tones tracing the graceful shapes of the figures.

Her affecting combination of the literary and the visual results in a powerful affirmation of individuality, creative expression and unconditional acceptance.

[7]Minh Lê, writing for The Horn Book Magazine, called attention to the small details present in Love's drawings, such as "a wary look in the mirror," and how they add depth to Julián's story.

[10] McKay also highlights the emotional state of the main character, going from proud to anxious as the story develops, and "filling readers with empathy and hope for his acceptance."