Under the terms of the deal, the US aircraft leasing giant has agreed to buy six A321-200s from Airbus that Thomas Cook will in turn lease from GE for 144 months.
Thomas Cook had originally placed a direct order with Airbus, although GECAS will now take direct ownership.
The 172-year old firm expects to receive four of the planes in the first quarter of 2015, with the remaining two expected to be delivered in the second quarter.
It has also agreed to lease an extra three A321-200 aircraft from GECAS for 144 months at market rates, with the first of the three to arrive in the first quarter of 2015.
Thomas Cook has struggled over the last two years with a slump in sales that has forced it to renegotiate bank loans and sell off planes and retail outlets to lighten its debt load.
Since travel industry outsider Harriet Green took over as chief executive last summer, she has identified more than £210m of cost savings through measures such as merging its airline businesses.
Green is targeting sales growth of at least 3.5 percent a year by 2015.