Polymeric phosphonium salts are an important class of polyelectrolytes that are currently gaining increasing interest due to their solution properties and reactivity. The successful controlled/living radical polymerization of a phosphonium salt-type monomer, 4-vinylbenzyltriphenylphosphonium tetrafluoroborate (4VBTPPBF4), under initiators for continuous activator regeneration atom transfer radical polymerization (ICAR ATRP) conditions employing a low concentration of catalyst is reported. After optimization of the reaction conditions, high monomer conversions to the polymeric phosphonium salt, poly4VBTPPBF4, were reached with very good polymerization control. The living character of the polymerizations was further evidenced via chain extension experiments that yielded either higher molecular weight homopolymers or block copolymers. It is also shown that poly4VBTPPBF4 can be efficiently converted to linear poly(4-vinylstyrene) using the Wittig olefination reaction.