Sierra was born in Decatur, GA, the eldest daughter of father Michael and mother Shontell McClain.

[10] In December 2005, while on the set of Tyler Perry's House of Payne, China introduced Sierra and Lauryn to a show producer and they performed a song for him.

They were then cast in the film Daddy's Little Girls (2007) as the James sisters, and Sierra guest starred in the series, Tyler Perry's House of Payne.

The next year, she starred as Carina in the film Shrink alongside Kevin Spacey and Keke Palmer.

[14] In 2016, McClain was cast and began starring as Nessa Parker, a recurring role, in the television series Empire (2016–2018).

[21] In December, the group performed their version of the song "Jingle Bell Rock" at the 2011 Disney Parks Christmas Day Parade.

In June 2020, the group McClain changed their name to "Thriii" and performed at Radio Disney Presents ARDYs Summer Playlist.

[42] When she was young, Sierra resided with her family near Atlanta, Georgia, but they later moved to Los Angeles for China's acting career.