This article offers a new theory of how extreme forms of imprisonment become normalized, using the development of life without parole (LWOP) in the Californian death penalty context over 40 years as an example. Normalization here refers to a punishment’s acceptability to the public, that is, what people think about severity. While this may be an empirical question that would take polling, this article proposes a theoretical model to explore how something like this might happen. The analysis builds on a literature that exposes how reforms can have perverse consequences on the punitive policies they mean to alter. These works however overlook reformers’ key role in shaping perceptions of severity and determining a punishment’s acceptability. To begin addressing this gap, this article draws on three concepts—visibility, denial and routinization—from theories on social acceptability to lay out a model by which reformers induce perceptions about severity. The article then applies the framework to a case study to show how the rhetoric, tactics and content privileged by specific actors produce normalizing mechanisms. Anti-death-penalty activists in California have contributed, this article argues, to making LWOP acceptable. This finding illuminates how extreme forms of imprisonment like LWOP can be normalized, in particular when set to replace something perceived to be more severe like the death penalty. It also enriches knowledge on the significant links between LWOP and anti-death-penalty activism. The novel frame finally has empirical, theoretical and policy purchase for extreme forms of imprisonment more generally.