Background: Platelets may be pivotal mediators of the thrombo-haemorrhagic complications of preeclampsia (PE), linking inflammation and thrombosis with endothelial and vascular dysfunction. While gestational hypertension (GH) falls within the spectrum of hypertensive complications of pregnancy and is a risk factor for preeclampsia, it is unclear what biomarkers distinguish PE from GH. Aim: To identify specific plasma and platelet thrombo-inflammatory biomarkers indicative of preeclampsia and distinguish PE from GH. Methods: We performed multiplex immunoassays, assessed platelet and plasma proteomics and metabolomics data of PE patients, and compared with non-pregnant (NP), healthy pregnant (PC) and GH participants. Results: We report plasma proteins upregulated, enriched plasma metabolites and proteins distinctly overexpressed in platelets of PE and GH compared to NP and PC. Whilst procoagulation in PC may be fibrinogen driven, Inter-Alpha-Trypsin Inhibitors ITIH2 and ITIH3 were enriched in hypertensive complications of pregnancy (PE and GH), and fibronectin and S100A8/9 may be major procoagulant agonists in PE but not GH. In addition, platelet leucine-rich repeat-containing protein 27 and 42 (LRRC27/42) subunits of volume-regulated VRAC anion channels were markedly overexpressed in preeclampsia and may contribute to the heightened glucose sensitivity and the pro-thrombotic tendency of this disorder. Additionally, our multiplex immunoassays confirmed previous reports of increases in preeclampsia plasma cytokines, including SDF-1α, which can directly activate platelets; but also, i-309 and CTACK cytokines, whose effects on platelets we explored using STRING analysis. Conclusion: We identified biomarkers that may be monitored for preeclampsia onset and progression, and distinguish PE from GH. Also, through protein-protein interactions analysis, we generated a new hypothesis for platelets’ contribution to the thrombo-inflammatory states of preeclampsia.