Kaczmarski, 26, was hitting .363/.413/.450 for the 51s in 24 games this season after missing the start of the season with an injury.
The left-handed hitting outfielder has experience at all three spots though is a better fit defensively at a corner outfield spot. He was the Mets ninth round pick in the 2015 draft.
Smith, 24, has a 2.88 ERA, 1.14 WHIP and 8.9 K.9 in 34.1 innings combined this year between Double-A Binghamton and Triple-A Vegas.
Smith has allowed only five home runs in 174 minor league innings and has a 2.02 ERA in that time.
The right-hander was acquired from the Rays last year in exchange for Lucas Duda. He was a third round pick of the Detroit Tigers in 2015.
Both Kaczmarski and Smith will have to be added to the Mets 40-man roster.