AllMusic critic Neil Z. Yeung thought that "Big Fish Theory cements Staples' status as one of the most talented and forward-thinking voices in rap in the late 2010s". The A.V. Clubs Clayton Purdom stated: "On Big Fish Theory, an album about the guilt that comes with transcending one's home, Staples finds a better language still." Liam Egan of Clash described the album as "a record that not only sees Vince taking risks and progressing forward as an artist, but also another astounding example of what hip-hop should and can be in 2017". Eric Renner Brown of Entertainment Weekly thought that Big Fish Theory "surpasses expectations, with incisive lyrics and beats that spurn current trends for a set that sounds unlike anything else in hip-hop right now". The Guardians Kate Hutchinson stated that the record "makes for a challenging, dystopian listen, the blade runner to everyone else's replicant".
