The 90210 star has been dating his fiancée Angela Stacy for three years, E! News reports.
He reportedly proposed during a trip to Paris last month.
Stacy's engagement ring is said to include a solitaire 4.2 carat diamond and a diamond band.
A source claimed that the couple are "perfect for each other".
As well as starring Liam in 90210, Lanter has appeared in shows like Commander In Chief and Heroes. He also played Edward Sullen in the Twilight parody Vampires Suck.