The 12,000-tonne Wave Ruler oil tanker will eventually go into service with the Royal Fleet Auxiliary next year.
Its launch marks the turnaround in fortunes for the Glasgow yard - which was put up for sale by former owners Kvaerner two years ago.
BAE Systems, the firm which took over at the Glasgow site, switched construction of the Wave Ruler from Barrow-in-Furness in Cumbria to the Clyde to keep the yard afloat.
Since then millions of pounds of further defence work have been secured by the yard, safeguarding hundreds of jobs.
In October, the yard won an order to build two Ministry of Defence vessels worth £150m.
Jamie Webster, GMB convener at the yard who has fought tirelessly to secure a future for the workforce, brought his daughter and two grandchildren along to savour the occasion.
He said: "I've been in shipbuilding 35 years and that's the most enjoyable launch I've ever been at, principally because we fought so hard to reach that.
Simon Kirby, BAE managing director, said: "This is an exciting day for everyone at the yard, for our customers, and for the Govan community.
"Wave Ruler has played a significant role in our efforts to try to ensure a future for shipbuilding on the Clyde."
Mr Kirby said plans were in place to ensure the long-term survival of the yard but some short-term problems still needed to be overcome.
"We've got long-term investment plans that we're very optimistic about and very positive about," he said.
"But we do have a short-term workload issue that we are working very hard to fill."