The additions raise the field so far for the year's first major championship on April 10-13 to 87 golfers.
Hojgaard will make his second Masters appearance after his 2024 debut, in which he was in the top six after each of the first three rounds and briefly led on Saturday before finishing tied for 16th.
World number 60 Hojgaard, 23, will join his twin brother, Rasmus, in the lineup. Rasmus will make his Masters debut in April. It will be the first time a pair of twins compete in the same Masters.
World number 71 Niemann, who plays in the Saudi-backed LIV Golf League, will make his sixth Masters start in April. He made the cut in his last four starts. He also made last year's field on a special invitation.
Niemann, 26, won LIV Golf events last year at Mayakoba in Mexico and at Jeddah and captured last month's Asian Tour Saudi International title. He shared ninth at the Paris Olympics, seventh at the DP World Tour Championship in Dubai and fifth as defending champion in the Australian Open.
"In support of Augusta National's efforts to develop interest in golf globally, deserving international players not otherwise qualified have been invited throughout the tournament's history," Ridley said.
"The tradition continues as we welcome Nicolai and Joaquin back to the Masters, as both players have showcased their talent while competing around the world. We look forward to their arrival this April."
