Nishikori is ranked outside the top 200 due to an elbow injury which stalled his progress last year, but the talented youngster's entry into the grass-court grand slam, which begins on June 21, is a much-needed boost.
The Shimane-born star, who lost in the first round of Queen's against Richard Gasquet on Monday, was just beginning to produce significant results before the elbow problem stalled his progress in 2009.
The 20-year-old's triumph at the Delray Beach event in 2008 was the first ATP title won by a Japanese man in nearly 16 years and he followed that by reaching the US Open fourth round.
Also given wildcards into the men's singles were British number three Jamie Baker, 254th in the ATP rankings and who was sidelined for six months by a life-threatening illness in 2008, Russia's Teimuraz Gabashvili - who reached the fourth round at the French Open - and Andrey Kuznetsov and German Nicolas Kiefer.
In the women's singles, 16-year-old Briton Laura Robson, who won the Wimbledon girls' title in 2008, has been given a wildcard.
Robson was beaten by former world number five Daniela Hantuchova in the first round at Wimbledon last year, but secured her first WTA Tour win on Monday when Stefanie Voegele retired injured when trailing by a set at Birmingham.
Fellow British players Heather Watson, the reigning US Open girls' champion, Katie O'Brien and Melanie South also received wildcards.
The organisers still have three wild cards to hand out on the men's side, and four to the women.