Akt (protein kinase B) is a key regulator in a variety of cellular processes such as glucose metabolism, cell survival, apoptosis, transcription, proliferation and cell migration. Its activity is aberrantly upregulated in a plethora of cancers, metabolic and immune disorders. More specific, time-resolved monitoring of key drivers of metabolism and proliferation in tissue specific contexts can be achieved in in vivo settings with the use of FRET-biosensor mice to track protein activity and the effect of therapeutic intervention. An Akt-FRET biosensor mouse was characterized to explore Akt activity in a variety of tissues and cancers. TCSPC multiphoton microscopy allowed for the imaging of this signalling biosensor in live mice by the application of optical windows. Akt activity was quantified in the pancreatic beta islets (RIP-Cre) and the native pancreas (Pdx1-Cre). Metabolic challenge in mice bearing optical windows over pancreatic islets, white fat or brown fat was performed to show Akt activity response. Elevated levels of Akt activity were mapped over the course of disease progression in PTEN loss driven pancreatic cancer models. PTENG129E/+ mutation or PTENfloxed/+ mice were assessed for Akt activity in several cancers such as lymphomas, adrenal, mammary and prostate cancer. In situ prostate spheroids cultures allowed for the systemic screening of Pi3K pathway inhibitors and their efficacy in conjunction with standard of care therapy such as enzalutamide. Mammary tumour cell lines expressing the AKT-FRET reporter allowed for the assessment of Akt inhibition in vitro over time in 2D and 3D invasion contexts. Optical window imaging showed optimal spatiotemporally mapped Akt inhibition by BKM-120 treatment in primary mammary tumours. In conclusion, the described Akt-FRET biosensor mouse can be applied to a wide range of metabolic, immune and cancer settings and used successfully in characterizing disease etiology and monitoring targeted treatment outcomes.