The organisation noted that the New Zealand charity, For Everyone, which Carter founded with fellow All Blacks Richie McCaw and Ali Williams in 2009, as part of the reason he was nominated. Now called iSport Foundation, the organisation funds small community projects between $500 and $5000 that are often difficult to find funding for.
Carter is also an ambassador for CanTeen, which supports young people with cancer.
Ronaldo was picked because he'd raised money for various causes. He'd donated more than US$83,000 to a 10-year-old fan in need of brain surgery and gave more than $165,000 to fund a cancer center in Portugal that treated his mother.
He has also used his fame as a global spokesperson for a variety of causes including childhood hunger, obesity and biodiversity.
Cena took home second place for granting nearly 500 wishes with the Make-A-Wish children's charity. He has also supported other organisations including Susan G. Komen to raise funds and awareness for breast cancer.
Williams is a UNICEF Goodwill Ambassador and supported the 1 in 11 campaign to support access to education this year.
"All over the world, athletes are using their platforms to rally fans around important causes," said Naomi Hirabayashi, chief marketing officer at DoSomething.org.
"DoSomething.org is proud to honor these athletes who are using their fame for good."
Others that round out the top 10 were former figure skater Kim Yuna, Brazilian footballer Neymar Junior, basketballer LeBron James, American footballer Heather O'Reilly, tennis player Maria Sharapova, American Little League Baseball pitcher Mo'ne Davis and American football cornerback Richard Sherman.
Ice dancers Meryl Davis & Charlie White are just ahead of Carter.
1. Cristiano Ronaldo
2. John Cena
3. Serena Williams
4. Yuna Kim
5. Neymar Jr.
6. LeBron James
7. Heather O'Reilly
8. Maria Sharapova
9. Mo'ne Davis
10. Richard Sherman
11. Meryl Davis & Charlie White
12. Dan Carter
13. Roman Reigns
14. Ronda Rousey
15. Lindsey Vonn
16. Tom Daley
17. Bethany Hamilton
18. Saina Nehwal
19. Paul Rabil
20. Shahid Afridi