In her first stint in the KSL, McGrath joins Harmanpreet Kaur (India) and Sune Luus (South Africa) as the Thunder’s third and final overseas signing for the season.
In the UK playing with Australia A since late June, McGrath is going into KSL match-fit and firing.
“I was really excited to get the opportunity to go over to England for the Australia A tour,” McGrath said.
“It’s my first time playing cricket here and it’s been good to test my game in different conditions.
“As it has now worked out, it’s been the perfect preparation ahead of my first Kia Super League spell with Lancashire Thunder.
“I have heard great things about Lancashire and I am looking forward to getting stuck in alongside my new teammates.”
Lancashire Head Coach Alex Blackwell played alongside McGrath in Australian colours and against the 23-year-old in the WBBL, while Blackwell captained the Sydney Thunder.
“(Tahlia) will take on the role of a senior player and has lots of experience in both franchise cricket and on the international stage,” Blackwell said.
“I believe she will complement our England girls and overseas signings in Harmanpreet and Sune really nicely.”
Following both England and overseas player announcements, the final Lancashire Thunder squad of 15 will be confirmed later this week.
Thunder kick off their campaign at home against fellow Striker Suzie Bates’ Southern Vipers on Tuesday 6 August at Liverpool Cricket Club.