JD Sports has agreed to acquire the remaining 40% of a Polish counterpart it does not already own.
The Greater Manchester-headquartered group first acquired 60% of Marketing Investment Group (MIG) in March 2021.
Since then, the JD sports brand has expanded across five countries in central and eastern Europe through 18 stores.
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In the year ended January 31, 2023, MIG generated revenues of approximately £270m.
Completion of the acquisition is subject to customary competition approval by the European Commission and "anticipated no later" than the fourth quarter of 2023.
JD Sports chief executive Régis Schultz said: "Acquiring the remaining 40% stake in MIG allows us to accelerate the development of JD in central and eastern Europe, the strong foundations for which have been established alongside the outgoing shareholders.
"Increasing JD's presence in the region through new store openings and further investment in our omnichannel capabilities is a key part of the strategic growth plan set out at our Capital Markets Day presentation.
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"The complementary Sizeer brand provides a strong platform for the MIG business and the JD brand has evidenced strong initial traction with the consumer, which we will continue to build upon.
"We look forward to closing the transaction and continuing an exciting journey with the local management team."
Before the initial deal in March 2021, MIG had been majority owned by brothers Andrzej and Zbigniew Grząka and operated 410 stores across nine European countries.
The latest deal comes after JD Sports announced last month that it was to acquire the remaining shares it didn't already hold in a Spanish company for over €500m.
JD Sports also revealed plans to open 50 stores across the Middle East after signing its first franchise deal.
In June, the group confirmed it still expects to report a profit of over £1bn for its current financial year after its sales continued to grow in recent months.