4iG did not disclose the value of the transaction but said it could close by the end of the year, pending clearance by competition authorities.
The company signed a term sheet to acquire Telenor Montenegro in July.
Telenor Montenegro has 413,000 subscribers and 436 base stations. It had sales of EUR 44 million in 2020.
4iG chairman-CEO Gellért Jászai said the acquisition is "an important step in the implementation of our strategy in the Western Balkans".
"The acquisition may open up additional opportunities for us in the region in the telecommunications and ICT markets," he added.