Danylo Halytskyi rebuilt and developed the Principality of Galicia–Volhynia, established by his father. He managed to unite a significant part of the ethnic Ukrainian lands under his rule, including the Principality of Kyiv and founded the cities of Chelm and Lviv. Danylo Halytskyi invited artisans and merchants from Poland, Germany, and other lands of Rus’ to settle there, and they worked for the benefit of the state under his patronage. 

Through the city of Dorohochyn, also rebuilt by Danylo, local merchants had access to one of the largest trading centres of that time — the Polish city of Torun.

To protect the Principality more effectively, he took care of fortifying old cities and constructing new-type fortresses (they were situated on hills with stone walls). During his rule, a reorganization of the Ukrainian army also occurred: infantry units were formed, and the cavalry was reequipped, focusing on heavy weaponry.

The main challenge for Danylo Halytskyi was the bloodthirsty Mongolian Golden Horde, which demanded tribute and military support from the Principality for their own campaigns.

Hoping for support and protection, Danylo accepted an offer of coronation from Pope Innocent IV in 1253. Unfortunately, the crown did not help to overcome the Golden Horde, but it did elevate his status to that of other crowned European rulers and left a mark in history.

Thanks to Danylo, the Principality of Galicia–Volhynia not only upheld the traditions of Ukrainian statehood but also solidified its further European-oriented development in its policies.

Another legacy of King Danylo is the blue and yellow colors for the national flag. The first use of such colors can be traced back to the coat of arms of the Principality of Galicia–Volhynia.

In Ukrainian history, Danylo Halytskyi will always stand side by side with distinguished representatives of his dynasty — Volodymyr the Great, Yaroslav the Wise, and Volodymyr Monomakh — but he will remain the only recognized king among princes.