Goal reported at the end of June that City were confident of warding off competing interest from Manchester United and Benfica by agreeing a deal worth €10 million (£8.5m) with Moreno's club Atletico Nacional.
The Premier League side had not agreed personal terms with the 19-year-old at that point, but have worked closely with the player's agent over the past fortnight and an agreement between all parties is now in place.
The completion of the move will be designed not to interfere with Nacional's Copa Libertadores campaign, with the Colombians on the brink of a final place after downing Sao Paulo 2-0 in Brazil in the first leg of the semi.
Moreno, who made his senior debut for the Colombia national team in March, is currently unlikely to qualify for a British work permit and City still intend to send him out on loan to Spain.
It is now understood that Deportivo La Coruna have emerged as front-runners to take the Medellin-born forward on a short-term deal once the paperwork on his move to the Etihad Stadium is completed.
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Moreno will therefore continue his football education away from City boss Pep Guardiola, as is likely to be the case for Ukrainian 19-year-old Oleksandr Zinchenko.
City closed a deal to sign Zinchenko last week but are keen to send the attacking midfielder on loan to a Champions League club, with Dutch title holders PSV said to be an option.
Both Zinchenko and Moreno have been earmarked by City scouts as potential stars for the future, however.
City moved quickly to tie up a deal for Zinchenko after his agent claimed in April that Borussia Dortmund were close to taking him to Germany.
And the Blues kept a close eye on Moreno as he competed for his country at the Copa America, where he scored his first senior international goal as Jose Pekerman's side eventually secured a third-placed finish.