118-26 amateur record. Won gold in 2007 and 2008 New England Golden Gloves Tournament.
The “Polish Prince” turned pro on DiBella Entertainment’s “Broadway Boxing” series, on August 6, 2008, winning a UD4 (all 40-36) over Raphael Luna.
Moved up to six-rounders in his seventh pro fight, then eight-rounders in his 10th pro bout.
Scored two knockouts, both in the third round, in 2009, against Aaron Chavez on March 19, and Norman Allen on Sept. 11.
On October 21, 2011, won a UD6 over Willie Villanueva, at Foxwoods Resort and Casino, in Mashantucket, CT.
In front of his local fan base at the House of Blues, in Boston, on May 24, 2012, Kielczweski earned a UD8 (all 79-73) over his most experienced foe, the 24-8 Ira Terry.
On September 29, 2012, Kielczweski scored a UD6 (60-54 twice, 59-55) over Jeremy McLaurin, back at Foxwoods.
To start 2013, Kielczweski scored his first knockout in three-and-a-half years, dropping Washington Hago twice with body shots, en route to a TKO2, on January 26 at Boston's TD Garden.
At the MGM Grand at Foxwoods, in Mashantucket, CT, on March 1, Kielczweski earned a unanimous decision over the always-tough Gil Garcia. Following eight exciting rounds, the scorecards read 80-72 twice, and 79-73, all for Kielczweski.