The younger Cahill, 18, has joined Ross Aloisi's Roar on a multi-year deal from Everton's academy, where he spent four years.
The midfielder notched three assists in nine games for Everton in the English Premier League's under-18 competition last season.
"We are pleased to announce the signing of Shae Cahill from Everton's world class academy," the Roar's chief executive Kaz Patafta said.
"Securing such a promising young midfielder is a testament to our club's new vision of integrating youthful talent into our squad and first team environment.
"Shae's addition promises an exciting era ahead for the Roar family."
Tim Cahill retired in 2019 as the Socceroos' all-time leading goalscorer, with 50 goals in 108 appearances for the national side - including scoring at three consecutive World Cups (2010, 2014 and 2018).
The attacking midfielder turned striker also netted 169 goals in 683 club games, most famously starring for Everton in England's top flight.
His tally includes 11 goals in 28 ALM games for Melbourne City in 2016 and 2017.
Cahill, 43, delighted in his son's first senior deal.
"Very proud of you my man @shaeloucahill," Cahill commented on the Roar's announcement post on Instagram.
"Wishing you all the best @brisbaneroarfc keep chasing your dreams."
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