The 'Hurt' hitmaker has sent a Valentine's card and letter to John Dalli, the European Commissioner for Health and Consumer Policy, to encourage him to support Humane Society International's CrueltyFree2013 campaign against animal testing.
She wrote: "Like most girls, I love make-up, but my ethical principles are also very important to me. No new lipstick, eye-liner or other cosmetics ingredient can ever be worth the suffering and death of defenceless animals forced to endure painful toxicity tests.
"These gentle animals are killed by the hundreds in some tests, despite the fact that manufacturing products free of new animal testing is perfectly possible through the use of thousands of existing, safe ingredients.
"Animals have suffered enough - if their pain has been deemed immoral within the EU, it must also be immoral outside the EU. To trade in their pain would be hypocrisy."
Leona is one of a number of stars, including the likes of Ricky Gervais, Dame Judi Dench, Melanie C, and Sir Roger Moore, to have signed the CrueltyFree2013 online petition.
In 2009, the European Union banned animal testing for cosmetics, but ingredients are still able to be tested on animals in other countries and sold in EU shops.