The Canadian rocker - who is an outspoken critic of President Donald Trump - applied for citizenship in order to vote in the 2020 presidential election and is thrilled the process has been completed in time.
Neil shared the news on his website alongside a photo of himself saluting next to a sign which read, "Democrats register to vote here."
He captioned the picture with American and Canadian flag emojis and wrote: "I'm happy to report I'm in!! Vote your conscience (sic)"
Neil also shared a video on Instagram, in which he waved two mini flags of America and Canada.
In the clip, he sang: "I'm proud to be a Cana-erican."
The 74-year-old singer revealed in November his citizenship bid had been delayed after he admitted to smoking marijuana.
He wrote on his website: "I want to be a dual citizen and vote.
"When I recently applied for American citizenship, I passed the test. It was a conversation where I was asked many questions. I answered them truthfully and passed.
"Recently however, I have been told that I must do another test, due to my use of marijuana and how some people who smoke it have exhibited a problem.
"The problem is defined in an April 19, 2019 addition under Attorney General Sessions. USCIS issued a Policy Alert which includes: 'An applicant who is involved in certain marijuana related activities may lack GMC (good moral character) if found to have violated federal law, even if such activity is not unlawful under applicable state or foreign laws.'
"I sincerely hope I have exhibited good moral character and will be able to vote my conscience on Donald J. Trump and his fellow American candidates, (as yet un-named).
"I will keep you posted, but I don't think I will be able to remain parked here during the proceedings."
Neil has been a frequent critic of President Trump.
In 2015, after the former 'Apprentice' star used Neil's song 'Rockin' in the Free World' during his presidential campaign announcement, the singer claimed he hadn't been authorised to use the track and endorsed Democratic rival Bernie Sanders.
And last year, the rocker - who is married to Darryl Hannah - criticised the president's response to the California wildfires after he blamed improper forestry management from the state.
Neil, who lost his home in the fires, wrote on his website: "California is vulnerable--not because of poor forest management as DT (our so-called president) would have us think. We are vulnerable because of Climate Change; the extreme weather events and our extended drought is part of it.
"Our temperatures are higher than ever here in our hottest summer on record.
""California is a paradise for us all. We are sad not to be able to defend it against Mother Nature's wrath."