AbstractReal‐time and in‐line transversal monitoring of ionizing radiation beams is a crucial task for several applications which span from medical treatments to particle accelerators in high energy physics. Here a flexible and large area device based on 2D hybrid perovskite thin films (phenylethylammonium lead bromide), fabricated onto a thin flexible polyimide substrate, able to map the transversal beam profile of high energy radiation beams is reported. The performance of this novel tool is here compared with the one offered by standard commercial large‐area technology, namely radiochromic sheets. The great potential of this class of devices is demonstrated by successfully mapping in real‐time a 5 MeV proton beam at fluxes between 108 and 1010 H+ s−1 cm−2, confirming the capability to operate in a radiation‐harsh environment without output signal saturation issues. The versatility and scalability of here proposed detecting system are demonstrated by the development of a multipixel array able to map in real‐time a 40 kVp X‐ray beam spot (dose rate 8 mGy s−1). Perovskite thin film‐based detectors are thus assessed as a very promising class of thin, flexible devices for real‐time, in‐line, large‐area, conformable, reusable, transparent, and low‐cost transversal beam monitoring of different ionizing radiation.