The Blues have announced a pre-contract agreement with Derry City for the 22-year-old, triggering on June 9.
The attacker will land at Fratton Park on a two-year deal for an undisclosed fee following a public pursuit.
However, Pompey must wait until the international transfer window opens on June 8 before the Republic of Ireland under-21 international's arrival is sanctioned.
Curtis visited Fratton Park last week to finalise personal terms, before the clubs continued negotiations.
He represents Kenny Jackett's maiden signing of the summer.
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