Motivation/problem statement: The glucagon-like peptide-1 receptor (GLP-1R) is expressed in various tissues such as the brain and pancreas. This class B G protein-coupled receptor (GPCR) is involved in the regulation of blood glucose levels and control of appetite. Despite being a major drug target for diabetes and obesity treatment, visualisation of the GLP-1R is limited to antibody detection, genetic manipulation or receptor-activating probes. Methods/procedure/approach: Various fluorophores were fused to Exendin4(9-39) to produce LUXendins. These fluorescent antagonists bind the GLP-1R in live tissue, with specificity confirmed using a novel Glp1r knock-out mouse line and by co-localisation with GLP-1R antibody. A mouse line was also generated expressing SNAP-tagged GLP-1R using CRISPR/Cas9 genome editing. Isolated pancreatic islets of these mice were treated with fluorescent SNAP-tag label to visualise the GLP-1R in situ, followed by receptor activation and trafficking after addition of agonist. Results: LUXendin645 (Cy5) intensely labelled the plasma membrane in live and fixed cells as well as pancreatic islets and brain. Most beta cells within an islet expressed the GLP-1R, whilst only ~5% of alpha cells were LUXendin+, as determined using Ins1Cre;mTmG reporter animals. STED imaging of MIN6 beta-cells labelled with LUXendin651 (SiR) revealed that endogenous GLP1R are organised into nanodomains, and variable diffusion at the plasma membrane was observed using single-molecule light microscopy. Five other LUXendins were also synthesised and tested, spanning green-near infrared spectra, with all variants producing bright membrane labelling of GLP1R. In SNAP_GLP1R knock-in mice, fluorescent SNAP-tag label co-localised with LUXendin and GLP-1R antibody. Thus, this mouse line can be used to visualise the GLP-1R in live tissue without stimulating the receptor. Addition of GLP-1R agonists allowed the monitoring of receptor activation and trafficking in situ. SNAP_GLP1R knock-in mice had normal body weight and responded to glucose like their wild type littermates. Conclusion/implications: LUXendins can be used in live tissue and be fixed to label endogenous GLP-1R and allows to study the receptor using confocal, two-photon and super-resolution microscopy in situ or in vivo. While LUXendins act as antagonists, linking fluorophores or dyes to SNAP_GLP-1R of the knock-in mouse line does not interfere with receptor activity and allows labelling post-fixation.   All animal research complied with the Animals (Scientific Procedures) Act 1986 of the U.K. Approval was granted by the University of Birmingham’s Animal Welfare and Ethical Review Body.