Nagy, who becomes an unrestricted free agent next northern summer, has been the Coyotes top offensive performer this season with 41 points on eight goals and 33 assists but became available when Phoenix was unable to sign the veteran Slovakian to a long term deal.
"Ladislav brings speed and skill to our hockey club and has proven to be a top-six NHL forward over his career," said Stars general manager Doug Armstrong on the team Web site (www.dallasstars.com). "We look for him to come in and make an immediate impact on our roster."
Now in his seventh NHL season, Nagy has 102 career goals with 169 assists. Tjarnqvist has just one goal and four points in 18 games with Dallas this season.