A native of Cornwall, Ontario, Lalonde earned his nickname by working in a local newsprint plant as a youth. He excelled at his two chosen sports and made his debut in organized hockey with Cornwall in 1905. This squad was known as the "Sweepers" because the players cleared the ice in lieu of renting it. Lalonde next moved to Woodstock, in southwestern Ontario, where his outstanding play at center caught the attention of several scouts.
Unexpected to Newsy, an offer came from the Sault Ste. Marie franchise in the International Hockey League, the first professional circuit in North America. The team across the river in Sault Ste. Marie, Michigan tried to obtain his services, but the Canadian Soo matched the American offer and kept the young star in town. In 1907 Lalonde joined the Toronto club of the newly formed Ontario Professional Hockey League. This was where he first gained wide attention by winning the scoring race with 29 goals in only nine matches. The Toronto squad captured the inaugural OPHL crown that year but lost out to the Montreal Wanderers in the Stanley Cup challenge.
Lalonde played a second year in Toronto before moving closer to his roots to suit up for the newly formed Montreal Canadiens National Hockey Association franchise in 1910. Partway through the season he was traded to the Renfrew Millionaires, but this only enhanced his performance. On March 11, 1910, he scored nine goals in one game, an NHA record that was never beaten and only equaled by Tommy Smith. He also won the league's inaugural scoring title.
In 1911-12, Lalonde headed west to play with the Vancouver Millionaires of the Pacific Coast Hockey Association, where he led the league with 27 goals. The next year he returned to the Canadiens and won another NHA scoring championship. His offensive gifts were a significant factor behind the franchise's first Stanley Cup title in 1915-16.
Lalonde remained with the Canadiens when the club joined the NHL in 1917-18. His scoring continued and he led all NHL scorers in 1918-19 and 1920-21. On January 19, 1920, he scored six goals in one game.
After a falling out with Canadiens owner Leo Dandurand, he was traded to the Saskatoon Sheiks for Aurel Joliat in a move that benefited both parties. In his first year in Saskatchewan, playing coach Lalonde added the Western Canada Hockey League scoring title to his list of accomplishments.
Lalonde returned to the NHL as coach of the New York Americans in 1927. He also coached the Ottawa Senators and Montreal Canadiens before leaving the game for good in 1935. He was inducted into the Hockey Hall of Fame in 1950.