The SD70M has a wide nose and a large comfort cab (officially known as the "North American Safety Cab"), allowing crew members to ride more comfortably inside of the locomotive than the older SD70 cab designs. There are two versions of this cab on SD70Ms, the Phase I, which was introduced on the SD60M, and is home on the SD80MAC and SD90MACs and the Phase II, which made a return to a more boxy design a la the original 3 window SD60M cabs. Though the Phase II cab has a two piece window matching the Phase I cab windows, the lines of the nose are boxy, with a taller square midsection for more headroom. The SD70M-2 line has what is considered the Phase III cab, as the windows are a rectangular window. Like the SD70, the SD70M also uses DC traction motors.

Starting in mid-2000, the SD70M was produced with SD45-style flared radiators allowing for the larger radiator cores needed for split-cooling (split-cooling is a feature that separates the coolant circuit for the prime mover and the circuit for the air pumps and turbocharger). There are two versions of this radiator, the older version with two large radiator panels per side, and the newer style with four square panels per side. This was due to the enactment of the EPA's Tier I environmental regulations. Production of the SD70M was replaced by the SD70M-2 in late 2004, as the EPA's Tier II regulations went into effect on January 1, 2005.

1,646 examples of this model locomotive were produced. SD70M models were produced with 4000 horsepower (2,980 kW) EMD Model 710 prime movers. Purchasers included CSX, New York Susquehanna & Western, Norfolk Southern and Southern Pacific, but the vast majority were purchased by Union Pacific.