He was three times Moscow champion (1947, 1956, and 1959), helped to train Vasily Smyslov to the World Championship, and made many significant contributions to chess openings.
Simagin's first important high-class result was second place in the 1946 Moscow Championship, with 11/15, behind winner David Bronstein.
In the 1947 Moscow Championship, he tied for top place with Bronstein and Georgy Rivinsky, with 9/14, and then won the playoff match-tournament.
In the semi-final at Vilnius 1949 (URSchsf-17), he again failed to move on with a tied 7th-8th place, at 9/17, with the winners being Furman, Vladas Mikėnas, and Alexey Sokolsky.
He improved at Tula 1950 (URSchsf-18) with 8/15 for a tied 5th-7th place, but still fell short, as the winners were Averbakh and Georgy Borisenko.
Chessmetrics ranks Simagin as #21 in the world from December 1946 to February 1947, and calculates his peak rating at 2650 in October 1949.
Simagin, along with Vladimir Makogonov, trained Vasily Smyslov for several years, leading to his World Championship title in 1957.
[citation needed] Bronstein had some very complimentary words in his book The Sorcerer's Apprentice (co-author Tom Furstenberg).
The Russian chess writer and master Lev Khariton wrote a touching tribute to Simagin on his chesscircle.net site.
Khariton wrote that Simagin was "modest and humble, never asking anything for himself in this life, he could stand by another man when the truth was at stake.