The Internet search provider released the data as part of its 13th annual Google Zeitgeist report but did not detail the number of searches per person, reported Aceshowbiz.
The top 10 most-searched queries are based on the volume of searches while trending queries are based on the highest amount of traffic over a sustained period in 2013 compared with 2012.
Walker died in a car crash on November 30 in LA, while Monteith was found dead in his hotel room in Vancouver on July 13.
The top 10 most searched terms in 2013 worldwide beside Walker, Mandela, and Monteith are iPhone 5s, Harlem Shake, Boston Marathon, Royal Baby, Samsung Galaxy s4, PlayStation 4 and North Korea.
Miley Cyrus is the most-searched person on Google this past year in the US, followed by Kim Kardashian, Drake, Beyonce Knowles, Justin Bieber, Selena Gomez, Katy Perry, Kanye West, Rihanna, and Taylor Swift. Cyrus' controversial stage act also led "What is twerking?" to top the most searched phrase beginning with "What is...".