The existing natural gas (NG) pipeline network is being considered to transport pure gaseous hydrogen (GH2) or blends of NG and GH2 for domestic and industrial energy needs, in an effort to reduce global CO2 emissions. The toughness and ductility of ferritic steels are reduced in the presence of GH2. In order to assess the viability of GH2 gas distribution via NG pipeline networks, it is necessary to understand the fatigue and fracture response of the materials in the network, including the various pipeline steels. Hydrogen-assisted fatigue crack growth (FCG) and fracture behavior of five different modern line pipe grade steels (X52, X70, X80, X100, and X120) were evaluated in high-purity GH2 at pressure of 210 bar, where the tensile strength increases with grade, X120 displaying the highest strength. The X52 and X70 steels feature ferrite with small amounts of pearlite in the microstructure. The X80 steel has a combination of polygonal and acicular ferrite, whereas the X100 and X120 steels contain fine ferritic and bainitic microstructures. The different pipeline steels exhibit similar accelerated FCG rates in the presence of GH2, irrespective of the strength and microstructural constituents. A significant reduction in the fracture resistance is observed for all the steels in GH2 as compared to air, although elastic-plastic fracture (J-R) behavior is maintained in GH2. Contrary to FCG rates, hydrogen-assisted fracture is affected by the microstructure and strength of the steel; higher strength steels exhibit lower fracture resistance and lower tearing modulus, analogous to the generally expected trends in air. Selected fracture surfaces are analyzed to rationalize the influence of microstructure and strength on hydrogen-assisted fracture of this class of steels.