Marmoush’s brace at the Etihad Stadium sealed a 5-1 aggregate semi-final victory, setting up a Wembley appearance for the holders.
"He gives us his special quality; his pace, his movements in behind, and his work ethic," Guardiola told Sky Sports. "His movements are really, really top. He has this incredible sense of goal."
The 26-year-old, who joined City from Eintracht Frankfurt for £59 million ($75 million) in January 2025, stepped up in the absence of the injured Erling Haaland to net his first brace for the club.
"The first goal is a bit lucky, but it's not lucky when you play with this passion, with this love. I'm really pleased for him," Guardiola added.
Guardiola noted that while Marmoush's minutes had been limited earlier in the season due to tactical shifts, his impact remains vital.
"Omar helped us a lot last season... this season we played a little bit different than the last one or two games, that’s why maybe he played fewer minutes," he said.
City will now look to defend their title in the final as Marmoush continues to establish himself as a key clinical option in Guardiola's rotation.
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