Aer Lingus Regional, which is operated by Aer Arann, carried just under 80,000 passengers in January, an increase of 23% on the same month last year.
Routes into and out of Dublin, from where Aer Lingus Regional serves cities such as Bristol, Cardiff and Edinburgh, were the main driver of growth.
Passenger numbers on its Dublin routes were up 43% year on year, while the carrier's Cork services also saw a return to growth with an 8% increase in passenger numbers.
Aer Lingus has been using the regional service to attract UK passengers onto transatlantic routes out of Ireland.
"These numbers are very encouraging, especially when you consider the challenging weather conditions across Ireland and the UK in January," commented Aer Arann's commercial director Simon Fagan.
"We made a range of strategic decisions last year to better position the airline for growth. Our focus on providing high frequency services, adding routes to the network and investing in a new aircraft fleet is resonating with passengers," he added.
Aer Arann will start its new Cork to Newcastle route next month, while a new route from Shannon Bristol will also commence. There are also plans to grow existing routes from Dublin, Mr Fagan said.