Ur-Nanshe's rule is significant as it stands at the beginning of a continuous documentary tradition illuminating the political events of the ED III period. He was likely of non-royal lineage, since in his inscriptions he refers to his father as one Gu-NI.DU without an accompanying royal title. The fact that the name does appear in offering lists from the time of the later kings Lugalanda and Uruinimgina suggests that Gu-NI.DU nevertheless held an important, possibily religious, office in Lagash (Bauer pg. 447).
Ur-Nanshe carried through a large number of building and renovation projects that have been recorded in his many royal inscriptions. These include a system of nine canals, the renovation of Nanshe's Sirara temple in Nina (or Nimin), and the renovation of Ningirsu's E-ninnu temple in Girsu. The unexpectedly wide scope of his building activity, especially of religious structures, has been taken as a sign of the hastening trend toward anthropomorphized deities whose status required a more substantial visual presence than the earlier tradition of divine emblems and totems (Bauer pg. 450). He also had wood brought from the state of Dilmun (modern Bahrain) via a special boat called the 'ma2-dilmun' for various building projects, especially temples.
Already before Ur-Nanshe a conflict between Lagash and Umma had broken out over the control of a fertile area between the two cities known as the Guedena. The historical roots of the dispute are not clear. A cone inscription of Enmetena (FAOS 05/1, Ent 28, A) frames them as a primordial issue involving the gods, where Enlil divides the Guedena between Ningirsu and Shara, the principle gods of Lagash and Umma respectively. Regardless of its origins, by the time of Ur-Nanshe the conflict grew to the point that an outsider, Mesalim the king of Kish, was called in to arbitrate the conflict, declaring a border that divided the land and marking it with a now lost inscription. This settlement did not keep the peace for long, however, as indicated by a text excavated from the Bagara Temple of Girsu in the 1970's (FAOS 05/1, Urn 51), which indicates Ur-Nanshe defeated Umma in battle and captured some of its leaders as prisoners.
The king also left behind a number of plates depicting himself, members of his family, and some of his followers. These early works illustrate several important elements of Mesopotamian iconography, such as the ruler standing with hands clasped as a typical depiction of piety (FAOS 05/1, Urn 21) or holding a basket on his head to signal participation in foundational building projects (FAOS 05/1, Urn 20).