The singer proposed to the One Tree Hill beauty as he celebrated his 28th birthday in Nashville, Tennessee - and Kramer said yes.
A statement issued to People.com reads: "We could not be happier! We are so excited to share this special time with our loved ones and cannot wait to start the rest of our lives together."
The couple, which recently moved in together, began dating last September (12).
The nuptials will be Gilbert's first, and Kramer's second - the actress-turned-singer was previously married to Christina Applegate's ex Johnathon Schaech, but they split a month after their wedding in 2010.