We started our investigation by using methyl 4-bromobenzoate (1) and 4-biphenyl acetic acid (2) with commercial gCN photocatalyst, NiBr2.glyme, and dtbbpy, with irradiation with a 390 nm Kessil lamp for 24 h, in order to achieve decarboxylative C-C bond formation. Initial results led us only to obtaining exclusive C-O (ester or phenol) bond formation or low reactivity in place of the desired C-C coupled product. Pleasingly, we found that using MeCN as solvent generated the desired product (3) in a moderate 32% yield, however, this was accompanied by the formation of unwanted ester, phenol and protodehalogenated side products. The presence of both the reduced carboxylic acid and its dimer in large quantities suggested that oxidation of the carboxylic acid by the photocatalyst and subsequent decarboxylation were taking place but the radical intermediate was participating in undesired sidereactions before combination with the nickel complex. We found that the heterogeneous nature of the reaction mixture led to some inconsistencies in mixing efficiency, and changing our reaction setup to ensure excellent stirring (see supporting information for details) led to an increased and reproducible reaction yield. Further systematic screening of our reaction parameters allowed us to identify optimal reaction conditions: using 1.5 equivalents of both the acid and base, 5 mol % of nickel with a 4,4'-diphenyl substituted bipyridyl ligand (dPh-bpy), and 1.0 equivalent of phthalimide additive, as described by MacMillan, led to isolation of 3 in a high 89% isolated yield (Table , Entry 1). DMF or DMSO as solvent led to no or low yields of the target product 3 (Table , Entry 2), and using K2CO3, CsHCO3, or BTMG as base generated product 3 in lower yields in comparison to Cs2CO3 (Table , Entry 3). When the reaction was performed with 1:1:1 stoichiometry between aryl halide, acid and base, a product yield of 70% was still observed, in conditions that would be preferential when using valuable carboxylic acids. 4methyl iodobenzoate performed similarly to the aryl bromides, albeit giving a lower yield of 63%, however, switching to 4-methylchlorobenzoate significantly reduced the formation of 3, generating 25% after 24 h. Performing the reaction with no phthalimide additive saw a reduction in yield to 45% (Table , Entry 6), and additional control experiments showed that in the absence of light, nickel or ligand, or base, no reactivity was observed, confirming the necessity of these components of the reaction. With our optimised conditions in hand, we investigated the scope of the carboxylic acid coupling partner (Scheme 2). We found that a wide range of benzylic carboxylic acids bearing either electron-donating or halogen substituents in the para-position were amenable to the reaction conditions, forming diarylmethane derivate products 4-7 in good to excellent yields. In comparison, acids bearing electron-withdrawing groups in the para-position were less reactive (8-10), although increasing the acid and base loading from 1.5 equiv to 3.0 equiv for products 9 and 10 increased the yield, generating 61% and 42% product yields respectively. Phenylacetic acid, bearing no substitution on the phenyl ring, generated product 11 in a 64% yield, and the addition of a fluorine atom in the α-position to the acid group had little effect on the yield, delivering product 12 in a 53% yield. In addition to phenyl substituted acetic acid derivatives, naphthalene (14, 81%), furan (15, 69%) and thiophene cores (16, 71%) were tolerated under the reaction conditions, generating the product in good yields. Indomethacin, a nonsteroidal anti-inflammatory drug containing a carboxylic acid group and a polysubsituted indole core, was able to be functionalised, generating product 17 in a 51% yield. Unfortunately, acids bearing substitution at the ortho-position of the phenyl ring, along with secondary and tertiary 2-phenylacetic acids, did not yield the desired products when subjected to the standard reaction conditions (for examples of incompatible coupling partners, see supporting information).