The actor, who plays Dr Jack Hodgins on the crime show, popped the question while the couple took a picturesque walk while on holiday in Cologne, Germany shortly after Christmas.
TJ shared a picture via Instagram showing the moment he got down on one knee in front of an emotional looking Leah.
He added the caption: "SHE SAID YES!!!"
TJ and Leah celebrated their engagement with a series of beautiful pictures immortalising the moment. Including one of them dressed in evening wear and standing within a ring of candles shaped like a heart.
He certainly raised the bar on engagement standards, didn't he?!
In case you're wondering who took all the pictures, TJ was sure to give his photographer pal a shout out for helping arrange the magical evening.
"If you ever need an amazing photographer to capture any event, Ulrik is awesome and helped me keep the big surprise 4 Leah!" (View his portfolio here).
TJ also thanked fans for their messages of congratulations, saying: "Wow! Thanks so much to ALL of you for your very appreciated "congrats!" Leah&I are having a blast! We couldn't be happier! Mwah!!!"
Congrats to TJ and Leah!