DeJonge was born in 1998 in Melbourne, Victoria, the daughter of Robyn and Rob DeJonge, a businessman. She moved to Perth, Western Australia with her parents at the age of five, where she grew up in Peppermint Grove. She has studied at the Presbyterian Ladies' College, Perth.
In 2015, DeJonge appeared in the Australian ABC's television drama series Hiding, on which she played one of the lead roles as Tara Swift / Shaneen Quigg. She played the co-lead role of Becca in the horror film The Visit, along with Ed Oxenbould. M. Night Shyamalan directed the film, which had its premiere on 31 August 2015, and was released on 11 September 2015 by Universal Pictures. In 2017, DeJonge starred as Alice Burbage in the TNT series, Will.
