The 22-year-old has signed a four-year contract, with the option of an additional year, after the newly promoted Premier League side agreed an undisclosed fee with Slovenian club Maribor.
Zambrano first arrived at the MKM Stadium on a season-long loan from Ecuadorian side LDU Quito and made eight appearances for the Tigers during the 2024-25 campaign.
That spell was cut short when the defensive midfielder was handed a 16-month suspension by South American confederation Conmebol in November 2024 for breaching anti-doping rules while still on the books at Quito.
The Court of Arbitration for Sport later reduced the ban to 12 months on appeal, and Zambrano returned to competitive football in November 2025 with Maribor, though injury restricted him to just seven appearances during his time in Slovenia.
Despite the disruption to his career over the past two years, Hull have moved to bring him back on a permanent basis, underlining the regard in which he was held during his brief initial spell at the club. Zambrano has been capped 14 times at Under-20 level by Ecuador and began his footballing education at the same academy as Chelsea's Moises Caicedo at Colorados Jaipadida.
He becomes Hull's second signing of the summer, following the arrival of 33-year-old goalkeeper Jack Butland from Rangers, as the club continues to build a squad capable of competing in the Premier League after securing promotion.
Zambrano's route back to English football has been an unusually eventful one. Having initially arrived with plenty of promise as a defensive midfielder capable of shielding the back line, his career was effectively put on hold for the best part of a year while the doping case worked its way through the appeals process.
That the ban was ultimately halved on review will offer some vindication to the player and those around him.
Now fully cleared to play after a stop-start return at Maribor, Zambrano arrives at Hull with a fresh four-year commitment and the chance to establish himself in the Premier League for the first time, having previously only sampled English football at Championship level.