Murray's last ATP event came in October 2019, when the former world number one beat Stan Wawrinka to win the Antwerp title.
The 33-year-old has been in action at the Battle of the Brits tournaments organised by brother Jamie in recent weeks, and he now enters a Cincinnati field which also includes Novak Djokovic, Rafael Nadal, plus 2019 winner Daniil Medvedev and Grigor Dimitrov.
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Currently the world number 129, Murray's presence at the Western & Southern Open boosts the likelihood he will feature at the US Open.
The ATP Masters 1000 event has been moved to New York due to the Covid-19 pandemic, and will take place from August 20-28, with the US Open then starting on August 31.
Americans Tommy Paul, Tennys Sandgren and Frances Tiafoe were also handed wild cards.
Andy Murray wants assurance on quarantine issues before US Open
Earlier on Monday it was reported that Murray was seeking assurances players would not face mandatory quarantine upon returning to Europe from the US Open.
Organisers United States Tennis Association (USTA) will set up a strict bio-security 'bubble' to minimise the risk of contracting the novel coronavirus during the Grand Slam, which will be played from August 31 to September 13.
Mandatory quarantine would rule out players' participation in other ATP and WTA clay court events scheduled in Europe before the French Open from the end of September.
The two major clay court events in the leadup to Roland Garros are in Madrid (September 13-20) and Rome (September 20-27).
While Spain does not require mandatory quarantine, Italy would need travellers to quarantine for 14 days if coming from the US. The USTA has said the organisers are working with relevant authorities to resolve issues.
"My understanding is that it would be sorted before we go to America. But things can change in the next 10 to 12 days," Murray told British media.
"Hopefully before we leave, the players will have the assurances that, when they come back from America, they won't have to quarantine for two weeks.
"If that is the case, and if you do well in the U.S. Open, you can't just arrive on the Sunday before the French Open starts on the Monday. That's not going to work."