Thornlie is an electoral district of the Legislative Assembly of Western Australia.

When Thornlie recreated it had a notional 1.8-point majority for the Labor Party (based on the results of the 2013 election), and was considered a marginal seat.

Sitting MP Sheila McHale contested and won the seat of Kenwick.

Upon its recreation prior to the 2017 state election, Thornlie had a notional 1.8-point majority for the Labor Party.

[2] Incumbent Gosnells MP Chris Tallentire contested Thornlie and won the seat with a 14% swing in his favour, thus making Thornlie a safe Labor seat.