Billie Eilish has always been a vegetarian. This is because, from a very young age, she has been quite conscious about her eating habits.
This consciousness never turned down but only reached a much higher level in 2014, when she made a hard decision of becoming a vegan by switching up her current diet completely and eliminating all animal-based foods from her diet.
Though the decision of turning a complete vegan was taken by her in 2014, she revealed it only in the year 2018 via a post made on Tumblr.
In that post, she highlighted that she loves animals and this planet and therefore does not find any sense in torturing the animals for self-pleasure when the animals are already existing and breathing. She also mentioned details about her body being Lactose Intolerant and how dairy was a disaster for her precious skin.
Also, Billie once revealed to Montreality that since she had grown up without consuming meat, she does not find turning vegan much difficult.
Apart from this, Billie also has certain views about encouraging Veganism among other people. For instance, in an Interview with the Dutch Outlet 3FM, she revealed that though she promotes veganism, she does not at all like forcing it. The reason she came out for this was that she hated telling people what to do, how to do.
According to her, just like she has her own reasons, beliefs, feelings towards this planet as well as the animals, other people also have their own views and feelings. So, rather than forcing, she just believes in encouraging Veganism.