The development of an interband cascade laser (ICL) based spectroscopic trace-gas sensor for the simultaneous detection of two atmospheric trace gases is reported. The sensor performance was evaluated using two ICLs capable of targeting formaldehyde (H_2CO) and ethane (C_2H_6). Minimum detection limits of 3.5 ppbV for H_2CO and 150 pptV for C_2H_6 was demonstrated with a 1 s integration time. The sensor was deployed for field measurements of H_2CO, and laboratory quantification of both formaldehyde and ethane are reported. A cross comparison of the atmospheric concentration data for H_2CO with data collected by a collocated commercial H_2CO sensor employing Hantzsch reaction based fluorometric detection was performed. These results show excellent agreement between these two different approaches for trace-gas quantification. In addition, laboratory experiments for dual gas quantification show accurate, fast response with no crosstalk between the two gas channels.