Two senior executives from tech company Stripe will also now not attend.
It has also been reported that actress Gillian Anderson has withdrawn from her speaking role at the conference.
Mr Cosgrave, the chief executive of Ireland-based Web Summit, issued an apology on Tuesday where he said he unreservedly condemns Hamas’s attack on October 7.
That followed a controversial post on X last Friday when he said he was “shocked at the rhetoric and actions of so many Western leaders and governments, with the exception in particular of Ireland’s government, who for once are doing the right thing.
“War crimes are war crimes even when committed by allies, and should be called out for what they are.”
Mr Cosgrave said his comments were to urge Israel not to cross the boundaries of international law in its response to Hamas atrocities.
In his later apology, he said: “I unequivocally support Israel’s right to exist and to defend itself. I unequivocally support a two-state solution.
“I understand that what I said, the timing of what I said, and the way it has been presented has caused profound hurt to many.
“To anyone who was hurt by my words, I apologise deeply.
“What is needed at this time is compassion, and I did not convey that.
“My aim is and always has been to strive for peace.
“Ultimately, I hope with all my heart that this can be achieved.”
Tickets for Web Summit range from 1,095 euro for general attendance up to 24,950 euro for a “chairperson” ticket which includes a “personal event fulfilment manager” and access to an exclusive lounge – with prices set to increase later this month.
The event aims to attract more than 70,000 people including “companies redefining the tech industry”.
On Friday, a spokeswoman for Google said: “We will no longer have a presence at Web Summit.”
It is understood Meta is also no longer attending the event.
A spokesman for Siemens said: “Following recent developments surrounding Web Summit, we have reviewed the situation and determined that Siemens will not attend in 2023.”
Intel said in a statement: “We can confirm that Intel has withdrawn from this year’s Web Summit.”