After fixing a broken pipe, the player is knocked into an underground cavern along with fellow builder Sam, where they fight the Rat King, the leader of the Bandirats, who are responsible for the town's recent water pollutions.

Gale also makes plans to build a museum and a tunnel to a neighboring city called Sandrock with the help of a visiting builder named Mint.

While examining an old mine to find out the cause of mysterious recent earthquakes, Mint and fellow builders Sam and Arlo get trapped in a cave-in and the player works with another worker named Remington to rescue them from a rogue robot called Rock-on.

The player later works with the other builders and Alliance agents Ursula Everglade, Ryder, and Ten to hunt for hidden relic keys in ancient ruins to unlock the way to the All Source.

Upon finding the base where the All Source is, Ursula, Ryder, and Ten betray and capture them with the help of Rogue Knight, revealing themselves to be a band of pirates called the Sky Sharks, but a reformed Tuss and Huss rescue them.

This forces Rogue Knight to flee while Ryder, Ten, and the Sky Sharks' mole are arrested and the All Source, whose actual name is Wendy, is reprogrammed to help the town.

[5] Miranda Sanchez of IGN called its core gameplay fun, but saying that each of its parts was lacking in some way, and that the game had "annoying audio bugs".

[2] Alex Fuller of RPGamer called the game "charming" and "a lovely place to spend time in", but also saying that it was too long, criticizing how "players have to wait for NPCs to decide to do something".

[21] Rich Meister of Destructoid said that while the world was "bright and full of charm", "waiting around for things to happen can get old pretty fast", and calling the game's mining "painfully dull".

[22] Philippa Warr of PC Gamer criticized the game's pacing, stating, "By being so slow, My Time At Portia both repels and appeals.

[24] Zoe Delahunty-Light of GamesRadar+ lauded the convincing NPCs, varied seasonal events, and sense of progression while taking issue with the loading times and lack of voice acting in cutscenes.

[25] Chris Scullion of Nintendo Life recommended the game after a patch was issued in order to fix its lengthy loading times.