In its final draft guidance, the regulator recommended Zydelig for patients whose leukaemia has come back less than two years following earlier treatment.
Earlier this year, NICE asked Gilead to provide additional information regarding the cost-effectiveness of the drug.
The company carried out new economic analysis and provided further discount, which was not revealed.
NICE health technology evaluation center director Carole Longson said: "We are delighted that Gilead Sciences responded to our consultation by providing further information for our independent appraisal committee and that they had agreed to provide idelalisib to the NHS at a reduced price in the initial submission.
"For people whose cancer has returned less than 2 years after their last treatment, their options are currently limited. With this new positive recommendation, the NHS will have another clinically effective option for treating adults with chronic lymphocytic leukaemia."
Zydelig is a phosphoinositide 3-kinase (PI3K) delta inhibitor and is used for the treatment of three B-cell blood cancers which include relapsed CLL, follicular lymphoma (FL) and small lymphocytic lymphoma (SLL).
The US Food and Drug Administration approved Zydelig to treat CLL, FL and SLL in July 2014.
Zydelig inhibits phosphoinositide 3-kinase delta, a main protein involved in the activation, viability, proliferation and migration of B-cells. The drug blocks the paths that cause B-cell viability.