The 22-year-old departed the Tractor Girls this summer after six years at the club, having previously been with Essex RTC, joining the Blues in the summer of 2020.
Hughes broke into the Town first-team during the 2021/22 campaign, before going on to make over 100 appearances for the club.
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Summer Hughes came through the Ipswich Town Women's academy. (Image: Ross Halls)
She was part of Joe Sheehan's title-winning side in 2025, the Bluesearning promotion to the second tier for the first time.
The versatile defender now links up with Pompey in a return to the third tier of women’s football.
On signing for the Hampshire side, Hughes said: “It feels really great to be joining the club.
"I definitely resonated with the club’s goals and their ambitions, and the playing style as well. A lot of my attributes suit it.”
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Pompey boss Jay Sadler added: "Summer has impressed us for a long time. She's athletic, competitive and exactly the type of full-back we wanted to add.
“I’m really excited to see what she will bring to the club for the upcoming season."