The main goal of this paper is to construct journal peer review as a scientific object of study based on historical research into its shaping. This paper is a first in a two-part series. Journal peer review performed in the natural sciences has been an object of study since at least 1830. Researchers mostly implicitly frame it as a rational system with expectations of rational decision-making. This in spite of research debunking rationality where journal peer review can yield low inter-rater reliability, be purportedly biased and conservative, and cannot readily detect fraud or misconduct. Furthermore, journal peer review is consistently presented as a process started in 1665 at the first journals and as holding a gatekeeper function for quality science. In contrast, socio-historical research portrays journal peer review as emulating previous social processes regulating what is to be considered as scientific knowledge (or not) (cf., inquisition, censorship) and early learned societies as engaged in peer review with a legal obligation under censorship. However, to date few researchers have sought to investigate journal peer review beyond a pre-constructed process or self-evident object of study based on common experience. Here I construct journal peer review as a scientific object of study with key analytical dimensions based on its structural properties. I use the theoretical concept of social form to capture how individuals relate around a particular content. For the social form of ‘boundary judgement’ (i.e., journal peer review), content refers to decisions from the judgement of scientific written texts held to account to an overarching knowledge system. Given its roots in censorship with its function of bounding science, I frame journal peer review as following precursor boundary judgement forms of inquisition and censorship. Constructing journal peer review as a scientific object of study contributes to improving it based on scientific understanding.