The Taoiseach intends to ask the Egyptian President to allow Ibrahim Halawa to return to Ireland following his trial on Monday.
Leo Varadkar has said he will phone President Sisi and it is his "hope and expectation" that Mr Halawa will be sent home as soon as possible.
The 21-year-old, from Firhouse in Dublin, has been in prison in Egypt since his arrest at a political protest in Cairo four years ago.
His sister Nosayba has said Ibrahim remains in high spirits.
"My brother was visiting him (Ibrahim) today and I spoke with my brother and he said Ibrahim's hopes were very very high," she said.
"I hope what we hear on Monday meets our expectation."
The Taoiseach has arranged a call with the Egyptian President where he will ask that Ibrahim Halawa be allowed to come home after his trial pic.twitter.com/4xYs1BeM6e— RTÉ News (@rtenews) August 26, 2017