The 26-year-old has emerged as one of head coach Roberto De Zerbi's most trusted players since the Italian's arrival, and has been described as "untouchable" in his plans.
Porro's current deal runs until 2028, but Tottenham are moving to extend it amid growing interest from elsewhere.
Manchester City have been credited with interest in the Spaniard, who progressed through City's academy as a youngster before later establishing himself in Spain and Portugal.
Real Madrid have also been linked, with reports in Spain suggesting the Spanish champions could look to Porro as a potential successor to Dani Carvajal.
However, Real Madrid have already moved to address that position by agreeing a deal to sign Denzel Dumfries from Inter Milan, reducing the likelihood of a move for Porro.
According to reports from Spain and England, including Diario AS, Tottenham have moved quickly to tie down their right-back once De Zerbi made his priorities clear.
Porro joined Tottenham from Sporting Lisbon in 2023 for a fee of around £40m, initially arriving on loan before the move was made permanent.
He has gone on to make over 150 appearances for the club, scoring 13 goals and registering 26 assists across all competitions.
This season, Porro contributed two goals and five assists across 47 matches in all competitions.
His form dipped during a difficult run under previous head coach Thomas Frank, with frustrations becoming increasingly visible as Tottenham struggled near the bottom of the table.
Since De Zerbi's appointment, Porro has returned to being one of the division's leading right-backs, delivering a string of strong performances as Tottenham secured their Premier League survival.
His display against Everton on the final day of the season, which helped confirm Tottenham's safety, was highlighted as one of his best of the campaign.
Tottenham finished 17th in the Premier League last season, securing their top-flight status in the final round of fixtures.
The extension comes as Tottenham continue to reshape their squad under De Zerbi, having already completed the signings of Andrew Robertson and Marcos Senesi this summer.
Yves Bissouma has been confirmed as a departure, while Cristian Romero and Radu Dragusin are also expected to leave the club in the coming weeks.
Porro is currently away with Spain at the World Cup, where he is expected to feature prominently at right-back under head coach Luis de la Fuente.
He has already won two assists in 18 appearances for the Spanish national team.
Before joining Sporting Lisbon, Porro came through at Girona, having earlier spent time in Manchester City's academy setup.
With Robertson, Senesi and now Porro all tied to longer-term deals, De Zerbi appears to be building the defensive spine of his Tottenham side around players he has identified as long-term assets.
For Porro, securing his future at Tottenham represents a vote of confidence from a manager who has helped revive his Premier League career within a matter of months.
The deal, once signed, would put to rest any speculation over his future and confirm Tottenham's intention to build their next era around their current core rather than start again from scratch.