The 24-year-old arrives from French side Amiens where he played 40 times, and has experience of a further 150 games in the Slovakian top flight with a variety of teams.
Flames’ boss Paul Dixon said: “Tomas is a good skater who can move the puck, but plays a strong defensive game.
“He is still a relatively young player, but with a good number of games in a world class league in Slovakia plus experience in France.
“We have no doubt he can be an impact player for us, and we are looking forward to getting him in the line-up when the season starts.”
Nechala added: “I am very happy to be a part of the Guildford Flames organisation and I have heard only positive things about the club.
“It will be an exciting new challenge for the team moving up to the top league and also a great test for me personally. I hope and wish that we have a successful season.”