The dentist arrived at work at 07:00 local time where a throng of media and a few protesters awaited him.
Employees were seen escorting Walter Palmer and patients into the surgery, as photographers swarmed the office.
In recent interviews, Walter Palmer has claimed that the hunt was legal and that he was shocked to hear the animal was famous.
Police were present as Walter Palmer parked his vehicle on a nearby street and walked into his office in Bloomington, Minnesota. A staff member clutched his arm as the pair pushed past a group of journalists.
One woman could be heard screaming “Extradite Palmer!”
Walter Palmer, 55, did not speak to the media on September 8, but did give an interview to the Minneapolis Star Tribune on September 6.
“I need to get back to treating my patients,” Walter Palmer said.
“My staff and my patients support me, and they want me back. That’s why I’m back.”
The killing of Cecil in July prompted a global uproar, which Walter Palmer has claimed led to “some safety issues” for his family.
Walter Palmer’s clinic and his home in nearby Eden Prairie became the site of protests, and his holiday home in Florida was vandalized.
Police did not consider the protesters.
Walter Palmer is believed to have been paid $50,000 to hunt a lion in Zimbabwe’s largest game reserve, but he says he was unaware it was so famous.
“If I had known this lion had a name and was important to the country or a study obviously I wouldn’t have taken it,” he said.
“Nobody in our hunting party knew before or after the name of this lion.”
Cecil was well known in the Hwange National Park and was being tracked with a GPS collar as part of a research program run by Oxford University.
The Zimbabwe’s safari organization has said the way in which Cecil was lured out of a national park was unethical and possibly illegal.
Initially, Zimbabwe sought to charge and extradite Walter Palmer, but the government’s interest in him has waned in recent weeks.
The Associated Press reported that government officials fear it could hamper a hunting industry that is lucrative and important for Zimbabwe.
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