Sergei Zhigalko was born in Minsk and is the younger brother of GM Andrey Zhigalko, who is also one of the top players in Belarus.
An International Master in 2004 and Grandmaster in 2007, Sergei was the 2003 U14 European champion and the 2006 U18 European champion. He came =1st-4th in the strong IV International Georgy Agzamov Memorial in Tashkent, Uzbekistan in March 2010. Sergei and Andrey played boards one and two for Belarus during the Chess Olympiad (2010) and the Chess Olympiad (2012). He scored 6.5/9 at the Chigorin Memorial 2010 placing 8th on count back. In the 2010 Ukraine club championship he scored 7/8 (+6 =2) for his team, which won the championship, for a performance rating of 2762. In 2011, he placed =1st with his brother Andrey at the Belarus National Championships, 2nd at the Moscow Open 2011 A - Young GM and =5th (11th on tiebreak) in the 12th European Individual Championship (2011), thereby qualifying for the World Cup (2011).
Zhigalko came =2nd in the GM tournament in Lublin in Poland, with 4.5/7, a half point behind Alexey Shirov, scored reasonably well in the Turkish Club Championship, came =4th at Lake Sevan 2011, and won the powerful Baku Open (2011) with 7/9 (TPR 2808). However, at the World Cup he lost in the first round to Uzbekistan's GM Anton Filippov. Subsequent mediocre results in the 7th Ugra Cup, in the Polish League and in the European Club Cup almost cost him his place in the world's top 100. He came =1st at the 15th Open International Bavarian Championship in October 2011. Slightly under-par results in the 2012 Belarus Championship (8/11) and in the Aeroflot Open (2012) (4.5/9) temporarily cost him his place in the top 100 in the March 2012 rating list, but a respectable 7/11 at the 13th European Individual Championship (2012) restored him to the top 100 in May 2012. =1st at the Nakhchivan Open 2012 with 6.5/9, scoring 7/10 playing first board for Belarus in the Chess Olympiad (2012) in Istanbul and then winning the Baku Open (2011) have restored his fortunes even further as can be seen from the improvement to his rating and ranking below. Unfortunately, 2012 wound up in disastrous style for Zhigalko as poor performances in the Governor's Cup in Khanty-Mansiysk and in the final rounds of the Chinese League deprived him of 31 rating points, costing him 30 rankings and nearly losing his spot in the top 100. Undaunted, Zhigalko entered the Belarussian Championship in January 2013 and easily won with 8/11 points, clawing back 5 rating points and 11 world rankings.
As at 1 May 2013, Zhigalko's classical rating was 2660 and he is ranked as Belarus's top player and number 83 in the world. His rapid rating was 2684 (world #43) and his blitz rating was 2682 (world #52).