Nitrogen stable isotopes (δ15N) of ice core nitrate of nitrate (NO3-) are often subject to various interpretations, associated with source, atmospheric, and/or post-depositional changes. Here, an analysis of a Mont-Blanc (French Alps) ice core was conducted to investigate δ15N(NO3-) records over the last 1000 years. We find that the glacially archived δ15N(NO3-) signal reliably preserves a record of NOx emission sources with limited post-emission isotopic changes. We use the δ15N record to reconstruct a history of NOx emissions and compare it with existing estimated NOx inventories for Western Europe. Notably, our ice-derived record suggests that inventories for the early 20th-century may have underestimated NOx emissions resulting from agriculture. During the 20th century, the δ15N value substantially decreased, which we attribute to the increasing emissions from oil combustion. Lastly, the ice core signal highlights the success of mitigation policies in reducing fossil fuel-induced NOx emissions, albeit 20 years later than anticipated.