From one whistleblower in exile to another in military prison: a birthday greeting. Edward Snowden marks the 27th birthday of Chelsea Manning on Wednesday with a personalized message that praises the WikiLeaks source for having “inspired an angry public”.

Since he astounded the world with his NSA revelations in June 2013, Snowden’s name has perhaps inevitably been associated with that of Manning, who had similarly astounded the world with the WikiLeaks trove of state secrets three years previously. In the pantheon of contemporary US official leakers, Snowden and Manning rank supreme – they were jointly nominated for the Nobel peace prize and Snowden referred to Manning in his early interviews, as “a classic whistleblower”.

Now Snowden has offered words of comfort for Manning as she marks her fifth birthday behind bars. From his own exile in Russia, the former NSA contractor thanks Manning for her “extraordinary act of service”, regretting that “it has come with such an unbelievable personal cost”.

He writes: “You have inspired an angry public to demand a government that is accountable for its perpetration of torture and other war crimes, for the true costs of its wars, and for conspiring in corruption around the world.”

Snowden’s greetings are among a slew of birthday messages from artists, writers and activists published by the Guardian. The group variously express admiration for her act of courage and hope that, with many more years of her sentence left to run, she might find some consolation in the knowledge that she is in the thoughts of others.

As the Nobel prize-winning novelist JM Coetzee puts it: “I’m sure it is not much fun spending your birthday behind bars, but I want to let you know that there are thousands and millions of people in the wider world who are thinking of you and wishing you well.”

Michael Stipe, formerly of REM, sends a handwritten note headlined: “Hey Patriot!!” He says “A lot of friends and supporters are thinking of you today.”

Filmmaker Terry Gilliam offers a cartoon of a wobbly figure tentatively stepping onto a tightrope over a cliff with the words: “Chelsea, your bravery has shown us much to be worried about. We are deeply in your debt.”

Another handwritten letter, with accompanying sketch, comes from the artist Molly Crabapple, who attended parts of Manning’s military trial at Fort Meade last year. Crabapple laments that she was unable to thank Manning there and then, “to hell with the rules of the court”.

Fashion designer Westwood adapts a ecological slogan: “What’s good for the planet is good for Chelsea.”

Further messages come from the Icelandic politician and former WikiLeaks volunteer Birgitta Jónsdóttir, philosopher Slavoj Žižek, graphic novelist Alan Moore, cartoonist Joe Sacco, rapper Lupe Fiasco, LGBT campaigner Peter Tatchell, trans author Billy Martin and poet Saul Williams.

Manning, who changed her name to Chelsea by petition in April as part of her gender transition, is serving a 35-year sentence for her transfer of massive databases of secret documents to WikiLeaks in 2010. The digital stash included videos of civilians being killed in Baghdad by a US attack helicopter, war logs from Iraq and Afghanistan that exposed the costs of America’s wars, and US embassy cables from around the world that helped instigate the Arab spring while embarrassing the Washington establishment.

Conditions in the military prison at Fort Leavenworth, Kansas, where Manning is held, are considerably better than those in Quantico military base in Virginia where she was first held in solitary confinement following her arrest in Iraq. But she continues to struggle with the US military authorities to allow her access to treatment for gender dysphoria, as she described in a recent Guardian article.

Though she is not allowed to communicate by phone or in person with the media, she continues to write for the Guardian and for the website of her support group. She also receives a stream of letters from the public, many of which receive replies.

•This story was updated on 16 December to correct Birgitta Jónsdóttir’s nationality to Icelandic.