The hosts looked set for a straightforward win when they led 3-0 with 15 minutes remaining but Norwich scored twice in a minute to set up a nervy finish.
But Sam Gallagher's first Premier League goal settled Southampton's nerves, and the result, leaving Norwich winless in seven away matches in the top flight.
Morgan Schneiderlin fired Southampton ahead after just five minutes, with Rickie Lambert and Jay Rodriguez netting after the interval to put Mauricio Pochettino's men well in control.
But Johan Elmander and Robert Snodgrass scored in quick succession to give the visitors hope late on, only to see it dashed by injury-time substitute Gallagher.
After just one home win from their previous eight in the league, Southampton coach Pochettino highlighted the importance of improving their form at St Mary's Stadium and his players responded well by taking an early lead.
Southampton began the second half with renewed focus and within five minutes Ruddy was forced into action as he tipped James Ward-Prowse's 20-yard effort around the post.
Pochettino's charges increased their advantage just before the hour mark as Lambert expertly cut inside Joseph Yobo before confidently finding the bottom-right corner.
First, Elmander pounced on Dejan Lovren's botched back-pass and prodded under Artur Boruc, before Snodgrass smashed in a rebound following a Ricky van Wolfswinkel effort.
Southampton re-opened a two-goal lead in stoppage time, though, as Gallagher collected Steven Davis' pass to score a personal landmark goal, moving the hosts up to eighth.
