A new 240-km long, deep seismic reflection profile (POLCRUST-01) was recently acquired in SE Poland crossing the East European Platform (EEP) margin south-east of the North-German–Polish Caledonides (NGPC). Here we document geophysical field work and subsequent data processing and modeling. Results obtained from reflection seismic data are augmented by results of the first-arrival tomography applied to co-located extended-offset refraction data, as well as potential field modeling and comparison with the available wide-angle reflection/refraction data. Our preferred model of the crustal structure, derived by integrating seismic, potential field and geological data, is composed of crustal blocks (terranes) separated by nearly-vertical faults. These are: (I) intact part of the EEP; (II) Łysogóry Terrane; (III) Małopolska Terrane; and (IV) Carpathian Mts. with their basement. Reflective lower crust of the EEP can be an inherited feature of crustal extension (rifting) or compressional tectonics acting at the cratonic margin. The Teisseyre–Tornquist Zone (TTZ) is depicted as a Caledonian transcurrent accretion zone corresponding with the near-vertical Tomaszów Fault, bounding the Łysogóry Terrane to the east. The crust of the Łysogóry Terrane suggests EEP affinity, although its middle/lower crust thickness is highly reduced. The Małopolska Terrane seems to be internally subdivided into blocks of different magnetic properties of the lower crust. The Carpathian frontal thrust is associated with a change in the rock properties in the deep basement (an unknown crustal block?) which is not visible in seismic data alone. The interpreted structure of the Caledonian terranes and their tectonic boundaries favors a transcurrent style of a crustal accretion along the central and SE Polish segments of the TTZ, implying a very complex nature of the Caledonian accretionary belt of Central Europe: from an array of terranes displaced along the TTZ to an accretionary wedge of the collisional NGPC orogen between NW Poland and southern North Sea area.