Ní Chróinín is originally from ‘An Choill Mhór’, in the Irish-speaking town of Béal Átha an Ghaorthaidh, although her family is originally from nearby Cúil Aodha Her interest in sean-nós singing arose after attending her first Oireachtas na Gaeilge event when she was ten years old. In her own words, "It was a result of the Oireachtas that I was given a chance to meet with some of the greatest singers, dancers, poets, composers and characters who have now passed on". In the following year, Ní Chróinín started singing lessons, and was particularly influenced by local singers such as Máire Ní Chéilleachair and Eoiní Maidhcí Ó Suilleabháin, from whom she was able to learn her songs. Nell's sisterMary Ann also encouraged her to start singing. As a teenager, she won prestigious sean-nós singing prizes, in particular winning in her age category at the Fleadh Cheoil na hÉireann in 2005 and 2006. In 2008, Ní Chróinín won a medal at the Oireachtas na Gaeilge competition, second place amongst the female singers under 35 years of age, and she returned in 2010 to win first place in the same category. Having now won the young women's category, she qualified to compete for the primary event of the Oireachtas, the ‘Corn Uí Riada’ in the following year. She took part as one of eighteen contestants in 2011, singing ‘Cath Chéim an Fhia’ and ‘An Cailín Aerach’, although Jimmy Ó Ceannabháin ultimately won the coveted top prize. In 2014, Nell won Corn Uí Riada and was both the youngest person ever to win it and the first person from Seán Ó Riada's home place of Múscraí to win it. The songs that she won with were 'Cuisle mo Chroí' and 'An Chóisire' and she sang 'Na Táilliúirí' upon winning the competition. Nell Ní Chróinín joined the bandDanú in 2016. She will be featured in their album, 'Ten Thousand Miles', coming in April 2018.
Over the years, Ní Chróinín has made several television appearances as a guest singer, generally on the Irish languagetelevision station TG4. She has sung on traditional music shows such as Geanntraí and Anam an Amhrán, and she was also the subject of an episode of Amhráin is Ansa Liom in 2010, a programme where a chosen traditional Irish singer sings and discusses four of their favourite pieces. In Ní Chróinín's case, she chose ‘An Lacha Bhacach’, ‘Cath Chéim an Fhia’, ‘Seán 's a Bhríste Leathair’ and ‘Táimse agus Máire’.