He is known as the co-creator of the Star Wars character Ren, and for his work on comic books such as the Marvel's Fearless Defenders series, the graphic novel Celtic Warrior: The Legend of Cú Chulainn, and the monthly series Spider-Man 2099.

[1] Sliney's career began in Irish and UK small press publications before moving to create art for Farscape and Star Wars comics.

[citation needed] From March 2020, during the COVID-19 pandemic in the Republic of Ireland, Sliney has presented short drawing lessons in the "We Will Draw" segment of RTÉ Television's Home School Hub.

[6][7] Sliney is a volunteer for the Royal National Lifeboat Institution (RNLI) based locally.

[9] He is also a long time Everton fan and has created art for them.