His research interests include merging and colliding galaxies, active galactic nuclei (AGN), and the star formation history of the universe.

He is the second of three children; his older sister, Grace, is a retired banker, and his younger brother, Henry, is a family physician.

He then held postdoctoral positions at Kitt Peak National Observatory and Columbia, where he conducted research on galaxy evolution and the star formation history of the universe.

[13] Since 2016, Liu has served on the Vera C. Rubin Observatory Science Advisory Committee,[14] where he is involved with galaxy evolution research.

[7] 2000: One Universe: at Home in the Cosmos (with Neil DeGrasse Tyson and Robert Irion)[16] 2004: The Handy Astronomy Answer Book[17] 2013: The Handy Astronomy Answer Book, Third Edition[18] 2017: StarTalk: everything you ever need to know about space travel, sci-fi, the human race, the universe, and beyond (with Neil DeGrasse Tyson)[19] 2019: 30-second universe: 50 most significant ideas, theories and events that sum up... everything (with Karen Masters and Sevil Salur)[20] 2020: The Handy Physics Answer Book[21] 2021: 30-Second Space Travel: 50 key ideas, inventions, and destinations that have inspired humanity toward the heavens (with Karen Masters and Allen Liu)[22] 2021: Intro to Physics for Babies [23] 2022: The Cosmos Explained: A history of the universe from its beginning to today and beyond[24] 2024: The Handy Quantum Physics Answer Book[25]