Gene duplication events play an important role in genome evolution; they can also create developmental strategies that differ between species. However, the functional contribution of duplicated genes in early human development and pluripotency is poorly understood. To address this knowledge gap, I investigated NANOGP1, which is a duplicated pseudogene of a key pluripotency factor called NANOG. NANOGP1 was chosen as a model for studying gene duplication in human pluripotency for several reasons. Firstly, NANOGP1 is an evolutionarily conserved duplicate in Hominidae that appears to have an intact coding sequence. The pseudogene is currently annotated as non-protein-coding, although no functional assays have been performed to test this. Secondly, upon investigating the expression of pseudogenes in human naïve pluripotent stem cells (PSCs), I found that NANOGP1 is among the top 1% of the highest expressed pseudogenes. Because high expression levels of NANOG are crucial for maintaining human pluripotency, I hypothesised that a duplicated copy of this important developmental regulator could have similar properties and might contribute to the regulation of human pluripotency. Gene expression profiling revealed that NANOG and NANOGP1 have overlapping but distinct expression patterns, both in human embryos and in PSC states. NANOGP1 is highly expressed in naïve pluripotent cells but is significantly downregulated in primed pluripotent cells, while NANOG expression levels do not differ to the same extent between the two pluripotent states. RNA splicing analysis predicted that NANOGP1 encodes a protein with an intact homeodomain and transactivation domain, but lacking part of the N-terminus. The divergent N-terminus is the main structural difference between NANOG and NANOGP1 and was therefore used in this study to distinguish between the two genes. Using CRISPR/Cas12a-mediated gene editing in naïve PSCs, I introduced an epitope tag at the start of the predicted protein sequence, and this enabled me to demonstrate for the first time that endogenous NANOGP1 encodes an expressed protein. The ability to be translated into the stable protein raised the possibility that NANOGP1 could have a functional role. To test this, I performed a series of assays and established that at least two key functional properties are conserved between NANOG and NANOGP1: gene autorepression, and the ability to promote primed-to-naïve PSC reprogramming. Alongside this, however, downregulating NANOGP1 expression using inducible CRISPRi in naïve PSCs did not lead to a differentiation phenotype, 4 which is in contrast to NANOG loss of function. Finally, using ChIP-seq, I showed that NANOGP1 shared a subset of chromatin binding sites with NANOG, and also, surprisingly, had a small number of unique, NANOG-independent sites particularly at the promoters of neural-associated genes. Overall, I conclude that NANOGP1, a previously overlooked duplicated copy of NANOG, is an expressed, protein-coding transcription factor in human naïve PSCs. Most of the CDS, and several of the functional properties, are conserved, implying that NANOGP1 could be supporting or cooperating with its ancestral gene copy in stabilising pluripotency. At the same time, differences in the N-terminal of the CDS, binding occupancy, and distinct expression patterns, could potentially contribute to functional diversification. These differences could have significant evolutionary consequences for creating species-specific developmental strategies, such as novel cell type-specific activity, expanded protein interaction networks and interplay with signalling pathways. Collectively, these potential new properties might extend functional potential and, hence, could encourage diversification of developmental mechanisms. Taken together, my work has demonstrated that NANOG/NANOGP1 duplication serves as a paradigm for exploring how pseudogenes could support their ancestral copies, as well as expand the evolutionary potential of conserved developmental programmes.