Born in Havertown, Pennsylvania, the midfielder qualifies for Ireland through her Cavan-born father (Sean) but required an international transfer having represented the United States at underage level.
Farrelly had been in contact with WNT Manager Vera Pauw over the last two years and was invited to train with the squad in Austin, Texas this week.
The 33-year-old, who plays in the NWSL with NJ/NY Gotham FC, will be added to the official squad for Saturday's game at Q2 Stadium, Austin and the follow-up in St. Louis on Tuesday, April 11 - both against World No 1 USA.
Ireland WNT Squad
Goalkeepers: Courtney Brosnan (Everton), Grace Moloney (Reading), Megan Walsh (Brighton & Hove Albion), Sophie Whitehouse (Lewes)
Defenders: Harriet Scott (Birmingham City), Jessie Stapleton (Shelbourne), Louise Quinn (Birmingham City), Aoife Mannion (Manchester United), Diane Caldwell (Reading), Claire O’Riordan (Celtic), Hayley Nolan (London City Lionesses), Tara O’Hanlon (Peamount United), Áine O’Gorman (Shamrock Rovers)
Midfielders: Katie McCabe (Arsenal), Denise O’Sullivan (North Carolina Courage), Megan Connolly (Brighton & Hove Albion), Jamie Finn (Birmingham City), Ruesha Littlejohn (Aston Villa), Lucy Quinn (Birmingham City), Ciara Grant (Hearts), Roma McLaughlin (Fortuna Hjorring), Sinead Farrelly (NJ/NY Gotham)
Forwards: Heather Payne (Florida State University), Abbie Larkin (Shamrock Rovers), Amber Barrett (Potsdam Turbine), Kyra Carusa (London City Lionesses), Marissa Sheva (Washington Spirit), Alannah McEvoy (Shamrock Rovers)
International Friendly
USA v Republic of Ireland
Saturday, April 8
KO 19:30 (Irish Time) / 13:30 (CT), 14:30 (ET)
Q2 Stadium, Austin, Texas
LIVE on RTÉ2
International Friendly
USA v Republic of Ireland
Tuesday, April 11
KO 00:30 (Irish Time) / 18:30 (CT), 19:30 (ET)
CITYPARK, St Louis, Missouri
LIVE on RTÉ2
