Megellas was born in Fond du Lac, Wisconsin, and attended Ripon College in the nearby town of Ripon. The attack on Pearl Harbor occurred midway through his senior year. He participated in the school's Reserve Officers' Training Corps program and, upon graduation in May 1942, received a commission as a second lieutenant in the U.S. Army.
Megellas was originally assigned to the Signal Corps, but grew tired of the required additional schooling and volunteered to become a paratrooper in order to see combat. He first experienced combat in the mountains outside Naples, Italy, near Venafro, where he was wounded and hospitalized. In October 1943, while the remainder of the 82nd Airborne departed Italy to recoup before the invasion of Normandy, the 504th PIR remained behind and took part in Operation Shingle. On January 22, 1944, the 504th took part in an amphibious assault at Anzio. The fighting took a heavy toll, Megellas being wounded again, It was not until April before the regiment was withdrawn. Due to the losses at Anzio, the 504th did not participate in the D-Day Normandy Landings. They did, however, parachute into the Netherlands as part of Operation Market Garden, the airborne invasion of that country.
Megellas took part in the crossing of the Waal River near Nijmegen, where the American forces crossed the river in flimsy boats while under heavy machine gun fire. During the day's fighting, Megellas single-handedly attacked a German observation post and machine gun nest. For these actions, he was awarded the U.S. military's second-highest decoration, the Distinguished Service Cross. Another member of the 504th PIR, Private John Towle, was posthumously awarded the Medal of Honor for his part in the battle. Towle was the only member of the 504th to be so honored.
In late December 1944, the regiment was rushed into the Battle of the Bulge. On January 28, 1945 Megellas' platoon was advancing towards Herresbach, Belgium. Struggling through heavy snow and freezing cold, they surprised 200 Germans who were advancing out of the town. Catching the Germans largely off-guard, the attack proved to be devastating, with the Americans killing and capturing a large number and causing many others to flee. As they prepared to assault the town, however, a German Mark V tank took aim at them. Megellas ran towards it, and disabled it with a single grenade. Climbing on top of it, he then dropped another grenade into the tank, eliminating the threat to his men. He then led his men as they cleared and seized the town, and not one of his men was killed or injured. He was nominated for the Medal of Honor shortly afterward, but the account of his actions was not included in the original battle reports, and he was instead awarded the Silver Star.
Throughout the war, Megellas served with Company H, 504 PIR, which he would later come to command. In January 1946, he led his company down Fifth Avenue in New York City in the Victory Parade.
In 1946, Megellas left the active Army with the rank of captain and served for a further 16 years in the Army Reserve. He retired as a lieutenant colonel. He wrote a memoir of his wartime experiences entitled All the Way to Berlin: A Paratrooper at War in Europe. Megellas made an unsuccessful run as a Democrat against William Van Pelt to represent Wisconsin's 6th District in 1960, and he served on the Fond du Lac city council until 1961. He was portrayed by John Ratzenberger in the 1977 film A Bridge Too Far. Megellas lives in Colleyville, Texas as of 2009. He turned 100 in March 2017.Order of Saint Maurice in 2008.
Dallas Military Ball's Meritorious Service Award in 2009.
DAR Medal of Honor in 2010.
He was also the first American to be decorated by the Government of the Netherlands when he was awarded the Military Order of William Orange Lanyard. Selected by General James Gavin as the most outstanding officer of the 82nd Airborne Division, it was presented to him by the Dutch Minister of War in Berlin in 1945.
On May 21, 2013, Congressman Tom Petri of Wisconsin introduced H.R.2082 in the United States House of Representatives to request the President award the Medal of Honor to Megellas for his 'above and beyond' heroism on January 28, 1945, during the Battle of the Bulge. Senator John Cornyn also introduced the 'companion bill' S.993 into the U.S. Senate on that date. Both bills remained in committee and expired with the effluxion of the 113th Congress on 3 January 2015. In January 2017 Senate and House bills were again re-introduced. The Senate Bill S.238 was sponsored by U.S. Senator Ron Johnson of Wisconsin. The House bill H.R. 751 was sponsored by 6th Wisconsin District U.S. Representative Glenn Grothman.