Volkswagen claimed the No 1 position with 2,137 registrations, a market share of 12.37%.
Toyota and Ford were in second and third position.
Commenting, Paul Burke, Operations Director for Volkswagen Ireland, said: "We are delighted with the strong start to 2013, which continues the momentum from last year.
"The level of interest in all our model range plus our 3 Offer is very strong. In addition, the new Golf has been in huge demand since launch and we expect sales to increase further as supply improves. At the moment we are selling every car we can get our hands on."
Volkswagen Ireland's strong performance is against the backdrop of an overall motoring industry that year-to-date is 18.54% down on 2012.
Black was the most popular car colour in January.