Thick-walled borosilicate glass containers are essential components in the chemical and medical industries. The proposed solution could facilitate reliable long-term storage of hazardous materials, addressing a significant challenge in these fields. Until now, welding thick-walled glass containers has primarily depended on thermal gas processes, which have inherent limitations. This study examines how laser intensity and scanning speed affect the welding process, introducing a novel laser welding method for thick-walled borosilicate glass containers without the need for additional material. Due to the absorption properties of glass when using CO2 laser radiation (10.6 µm), the welding process is driven by heat conduction, a limitation that becomes particularly pronounced when welding thick butt joints. A glass bottom with an interference fit is welded to a glass tube of the same wall thickness using a CO2 laser, utilizing gravitational force to sink the softened glass bottom into the tube. This method significantly mitigates the limitations imposed by the restricted optical penetration depth of CO2 lasers. Microscopic images have demonstrated that the formation of micro gaps between the tube and bottom can be effectively prevented in the joining zone, while micro-CT images revealed a bubble-free fusion bond. Furthermore, leak-tightness is confirmed through a vacuum test, and mechanical stability is validated via external uniaxial compressive stress. The chemical resistance of the welded joint, crucial for assessing long-term stability, is investigated by storage in brine. This innovative, gravity-assisted laser welding method represents a fundamental advancement, providing a robust solution for producing thick-walled borosilicate glass containers.