The 22-year-old has become an integral player for Ruben Amorim's side since arriving from Famalicao in 2021 and attracted the attention of several top European clubs.
Chelsea were believed to have been closing in on the signing of Ugarte earlier this summer, while Aston Villa and Liverpool were also strongly linked with a move.
However, PSG moved quickest to trigger the €60m (£51.3m) release clause in Ugarte's contract, beating their Premier League rivals to his signature in the process.
Ugarte has already completed his PSG medical and agreed terms on a five-year deal until the summer of 2028, but an announcement has apparently been delayed until July 1.
Next month was seemingly too long a wait for Ugarte to announce his big-money move, though, as he confirmed his switch to Paris to reporters after Uruguay's recent 4-1 friendly win over Nicaragua.
The 22-year-old hailed PSG as a "giant" club and admitted that the news had not quite sunk in, although he is disappointed not to be sharing a dressing room with Lionel Messi, who is confirmed to be leaving for MLS side Inter Miami.
"The truth is that now we have to rest a little and then start with everything at PSG. I'm going to a giant club, I haven't even fully realized that yet, but I'm going to try to start with everything," Record quotes Ugarte as saying.
"It's true that Messi is leaving. It would have been incredible to play with him, but these are football things. But I'm very happy."
Ugarte leaves Sporting having scored one goal and set up three more in 85 appearances for the Portuguese giants, including one assist from 47 games in a defensive role during the 2022-23 season.
The 22-year-old won the Taca da Liga in his debut season with Sporting and also started all six of their Champions League group games in the most recent campaign, but he picked up a whopping 16 yellow cards and was sent off in the Europa League against Arsenal.
As well as Ugarte, PSG are also understood to have completed a deal to sign Real Madrid attacker Marco Asensio on a free transfer, but the Spaniard's arrival may not be announced for another couple of weeks as well.
Mallorca playmaker Lee Kang-in and Benfica starlet Cher Ndour are reportedly close to joining the French champions as well, as football advisor Luis Campos looks to add more young talent to the Parc des Princes ranks.
Despite adding to their midfield ranks with the signings of Vitinha, Fabian Ruiz, Carlos Soler and Renato Sanches last season, PSG only finished one point better off than Lens at the top of the Ligue 1 table while going out in the last 16 of the Champions League for the fifth time in seven seasons.
Head coach Christophe Galtier is expected to be sacked as a result, while Kylian Mbappe could also be offloaded after telling PSG in a letter that he would not extend his contract beyond 2024, but the Frenchman has affirmed that he plans to stay for next season.