A fully automated setup was developed for preparing whole blood samples using a Tecan Evo workstation. By integrating several add-ons to the robotic platform, the flexible setup was able to prepare samples from sample tubes to a 96-well sample plate ready for injection on liquid chromatography–mass spectrometry using several preparation techniques, including protein precipitation, solid-phase extraction and centrifugation, without any manual intervention. Pipetting of a known aliquot of whole blood was achieved by integrating a balance and performing gravimetric measurements. The system was able to handle 1,073 of 1,092 (98.3%) samples of whole blood from forensic material, including postmortem samples, without any need for repeating sample preparation. Only three samples required special treatment such as dilution. The addition of internal and calibration standards were validated by pipetting a solution of Orange G and measuring the weight and absorbance. Internal standard (20 µL) was added in a multi-pipetting sequence with an accuracy of 99.9% and imprecision (coefficient of variation) of 1.6%. Calibration standards were added with high accuracy at volumes as low as 6.00 µL (±0.21 µL). The general setup of the offline sample preparation and key validation parameters of a quantitative analysis of Δ⁹-tetrahydrocannabinol is presented.