In automotive industries, pulsed laser welding has been gaining importance for joining of thin sheet materials for various reasons, e.g., no use of any filler material, precise control over heat input, penetration depth, molten pool shape and short welding cycle. However, improper choice of heat input can lead to the development of weld defects. Hence, the current study is aimed to comprehend the influence of heat input (32.5, 56.25, 72.22 and 92.22 J/mm) on the weld thermal cycle, microstructural evolution and tensile deformation behavior of Nd:YAG pulsed laser-welded dual-phase (DP 780) steel joints in butt configuration. The effect of pulsation on the weld thermal cycles and the corresponding microstructural changes has been studied. It is estimated that the temperatures in the fusion zone (FZ) ranges from 1759 to 1891 K for 32.5 J/mm heat input and 1964 to 2116 K for 72.22 J/mm heat input welds. Depending on heat input microstructures in the FZ containing martensite, bainite and ferrite are changed due to change in the peak temperatures and the cooling rates. Due to softening of FZ and heat-affected zone by tempering of martensite and because of ferrite grain coarsening the yield strength, tensile strength and uniform elongation decreased with an increase of heat input. All welded joints failed in the softened heat-affected zone, and it was found that the amount and distribution of tempered martensite altered the void nucleation mechanism during the tensile deformation.