The precision and accuracy of an isotope ratio mass spectrometry (IRMS) laboratory and the quality of its scientific output directly depend on the quality of the reference materials used for calibration. However, the specification and characterization of the in-house reference material and analytical details of the laboratory routine are rarely published or accompanied in the scientific studies that rely on IRMS measurements. Here we describe the development of a new in-house laboratory reference material (SHP2L) used for normalizing measurements of carbon and oxygen stable isotopes (δ¹³C and δ¹⁸O) of carbonate material at the newly formed Paleoceanography and Paleoclimatology Laboratory (P2L). The analytical setup consists in a Thermo™ MAT253 coupled to a Thermo™ Kiel IV carbonate device. The equipment is stable in the long term (precision better than 0.1‰ over a two-months period) and ensures analytical precision (sample-to-sample, 1σ) better than 0.04‰ for δ¹³C and 0.07‰ for δ¹⁸O, down to masses of 30 μg. The material chosen for the production of the SHP2L is a calcium carbonate plate (about 800 cm³ to 2.1 kg) from the German Jurassic Solnhofen Formation. The isotopic homogeneity was assessed by taking 25 regularly spaced samples from both sides of the plate. The standard deviation of these samples were less than 0.11‰ for both δ¹³C and δ¹⁸O. The plate was then fragmented, ground and sieved to isolate the 63–124 μm grain-size fraction. The chemical and mineralogical quality of the SHP2L was established by X-ray fluorescence and diffraction respectively, which show predominantly calcium carbonate, with negligible amounts of other constituents in purely calcite mineralogical phase. Batches of ca. 50 samples from the 63–124 μm fraction were analyzed for δ¹³C and δ¹⁸O in three laboratories. Established SHP2L isotopic composition is −0.766 ± 0.042‰ for δ¹³C e −5.741 ± 0.064‰ for δ¹⁸O. The SHP2L proved to be a homogeneous reference material for δ¹³C and δ¹⁸O stable isotopes analyses. The methodological template for production of a carbonate working standard is illustrated herein. The SHP2L is available for distribution upon request to the first author.