The results of research on determining the influence of pressure (from 45 to 113 MPa) on the compaction parameters of milk thistle straw (Sylibum marianum) are presented. Raw biomass and biomass containing the addition of a binder in the form of calcium lignosulfonate were investigated. Compaction was carried out using a Z020/TN2S Zwick universal testing machine and a pressing unit with a closed die. It was found that with increasing pressure, the density of material in the chamber and the density of the briquette rises (on average by 33.8%), and the mechanical strength of the finished product grows almost 3.5 times. Increasing the compaction pressure augments the compaction energy demand by an average of 84%. It was shown that the addition of binder increases the density of the briquette (by 22% on average) and raises the mechanical strength by 150% on average.