Determination of organophosphorus fire retardants and plasticizers at trace levels in wastewater is described. In this work, microwave assisted extraction (MAE) and solid-phase microextraction (SPME) are used for sample preparation to extract and preconcentrate the analytes, followed by analysis by gas chromatography coupled to inductively coupled plasma mass spectrometry (GC-ICP-MS) for phosphorus-specific detection. Gas chromatography coupled to time of flight mass spectrometry (GC-TOF-MS) was used to confirm the organphosphorus fire retardants in wastewater. The detection limits of organophosphorus fire retardants (OPFRs) were 29 ng L−1 for tri-n-butyl phosphate (TnBP), 45 ng for L−1 for tris(2-butoxyethyl)phosphate (TBEP), and 50 ng L−1 for tris(2-ethylhexyl)phosphate (TEHP). Optimized extraction conditions were performed at 65 °C for 30 min and with 10% NaCl. Application of MAE during the sample preparation prior to the SPME allowed the detection of tris(2-ethylhexyl) phosphate, which has been difficult to determine in previous work. Application of the method to wastewater samples resulted in detecting 3.1 μg L−1 P from TnBP, 5.0 μg L−1 P from TBEP, and 4.0 μg L−1 P from TEHP. The presence of these compounds were also confirmed by SPME-GC-TOF-MS.