The Portuguese centre-back initially arrived in Germany on loan from Porto in 2022, before the move was made permanent, and made 25 appearances for Union Berlin last season.
Reports of interest from Lazio first surfaced as far back as January, when the Serie A club's sporting director claimed an agreement was in place, only for Leite's representatives to publicly deny any such understanding at the time. With his contract now having run down completely, the 27-year-old was free to negotiate with clubs outside Germany and has settled on a move to Rome.
According to Romano, the deal is expected to see Leite sign a three-year contract running until the summer of 2029, with an additional club option for a further season included in the terms.
The move brings to an end a five-year saga around Leite's future that has, at various points, also linked him with AC Milan and RB Leipzig, both of whom were said to have made approaches for the defender during his time in the German capital.
Lazio finished ninth in Serie A last season and have made an underwhelming start to the current campaign, winning just two of their opening matches. Leite's arrival adds defensive experience and Bundesliga pedigree to Gennaro Gattuso's squad as the club looks to close the gap on Italy's leading sides.
Having come through Porto's academy before loan spells at Braga and then Union Berlin, Leite has developed into a well-travelled, experienced defender capable of playing across various backline configurations, attributes that should serve him well as he adapts to Serie A football.
The free transfer represents a shrewd piece of business for Lazio, who secure an established international defender without paying a fee, even if the protracted nature of the saga means the move arrives considerably later than either party might once have hoped.
Lazio have endured a turbulent 12 months off the pitch, having been unable to register new signings during the 2025 summer window because of financial irregularities, a restriction that contributed to Sarri's eventual departure for Atalanta at the end of last season.
Gattuso, who took over in June following his own exit from the Italy national team job, now inherits a squad short on depth in several areas, making the free acquisition of an experienced international defender like Leite a particularly valuable piece of business regardless of the fee involved.