Gleiss Lutz advised longstanding client Blackstone on its first investment in a government-controlled company.
The US private equity group was selected by the German government as the preferred bidder for a 4.5 per cent, E2.68bn (£1.5bn) stake in Deutsche Telekom.
Blackstone established a new company, Green Park 1 Acquisition, for the acquisition, which gives the group a seat on the Deutsche Telekom board.
The private equity group bought its holding from KfW Bank, the German development bank, and it makes Blackstone the third-largest shareholder in Deutsche Telekom after KfW Bank and the German government. It is not known how Blackstone will finance the acquisition.
Partners Christian Cascante and Jan Bauer led the Gleiss team, which also included employment, regulatory and tax partners.
Gleiss is Blackstone's regular German adviser. In 2004 the firm acted for the private equity house on its takeover of Celanese, the biggest takeover of that year and Germany's largest public leveraged buyout to date.
Simpson Thacher & Bartlett, led by London corporate partners Michael Wolfson and Ryerson Symons, advised Blackstone on US aspects of the deal.
Linklaters, led by Frankfurt banking and capital markets partner Herbert Harrer, advised KfW Bank. The firm also advised on the bank's sale of E5bn (£2.8bn) in bonds exchangeable into Deutsche Telekom.
Thomas Bulgrin and Andreas Benckendorff led KfW Bank's in-house team.