Johnson, who was stripped of his 100 metre gold medal at the 1988 Seoul Olympics after testing positive for steroids, said other athletes should look at themselves before casting judgment.
"People shouldn't be pointing fingers, they should be worrying if they pass the test," Johnson told ITV News. "Many people who pointed fingers at me tested positive later on.
"He deserves a second chance," added the former athlete. "There are many people who've done bad things in the world but we don't know."
Chambers was last week cleared for the London Olympics after the British Olympic Association officially rescinded its lifetime ban for athletes found guilty of doping offences.
The formality followed the Court of Arbitration for Sport (CAS) ruling which declared the BOA's controversial bye-law to be in direct contravention of the World Anti-Doping Agency (WADA) code.
Johnson said he would not be watching the London Games and hit out at British athletes who said Chambers should not be allowed to race.
"Who are they to decide whether he competes or not?", he asked. "You don't see those guys 24/7, what they do in the middle of the night".
Jamaican competitor Asafa Powell also backed London-born Chambers, who is set to compete against world-record holder Usain Bolt in the Czech Republic on Friday.
"He really deserves this and he's a real cool guy," Powell told ITV News.
"The Olympics is in London and I'm sure they want someone in the final," he added. "I think Dwain is the best chance".
(For more sports news and updates, follow Ahram Online Sports on Twitter: @AO Sports)