Which Substack writers gained the largest subscriber growth in 2025?
Executive summary
The reporting does not provide a single, definitive leaderboard of 2025’s fastest-growing Substack writers, but multiple sources point to a mix of legacy media stars, platform-native viral winners, and a handful of importers who moved large external audiences onto Substack — with examples including Heather Cox Richardson, Jim Acosta, Justin Welsh and several newer publications that surpassed half a million subscribers after importing audiences [1] [2] [3]. Any attempt to name “the largest subscriber growth” must account for Substack’s tools for importing lists and internal discovery changes in 2025 that make raw growth figures ambiguous without company-released rankings [3] [4].
1. High-profile migrations produced some of the clearest spikes
A visible pattern in 2025 was established journalists and media figures moving to Substack and acquiring large audiences quickly: former CNN anchor Jim Acosta reportedly amassed over 10,000 paid subscribers within weeks of joining, an example of instant paid-audience conversion when a recognizable name moves platforms [2]. Likewise, long-established newsletter stars such as Heather Cox Richardson continued to sit at the top of overall subscriber counts — her Letters from an American is cited as having grown to over 1.3 million subscribers, underscoring that celebrity and trust still translate into large subscriber bases [1].
2. Rapid bestsellers and viral Notes explained many meteoric rises
Substack’s internal mechanisms — especially the bestseller/leaderboard signals and the Notes feature — propelled some writers to fast growth in 2025; Justin Welsh became a Substack Bestseller within 48 hours of launching, demonstrating how platform ranking signals and existing audience mobilization can produce extreme short-term growth [2]. The company’s leaderboards and bestseller badge system were explicitly linked to paid-subscription growth and often amplified creators who hit a viral moment on Notes or other discovery features [5].
3. Imported audiences complicate “organic” growth claims
Multiple observers flagged that newer publications exceeding 500,000 total subscribers in 2025 often did so by importing pre-existing lists from other platforms, a capability Substack makes easy and which compresses years of growth into a short window [3]. That practice means headline growth numbers can reflect audience migration more than platform-driven discovery, and any claim about the “largest growth” should distinguish between imported list moves and organically acquired Substack subscribers [3].
4. Platform-level shifts amplified internal discovery in 2025
Substack reported that a huge share of new subscriptions in 2025 came from inside the app: one account described Substack saying 32 million new subscribers were added via internal discovery over a recent three-month span, signaling that recommendation features began driving massive on-platform growth independent of external promotion [4]. That shift implies some of the year’s fastest growth stories were the product of algorithmic or in-app recommendation dynamics rather than author name recognition alone [4].
5. Money, ranking and strategy: the quiet winners and the visible ones
The CEO signaled that more than 50 Substack authors were making over $1 million a year by mid-2025, a data point used by analysts to infer which publications had both sizable paid subscriber bases and strong revenue trajectories, though the company’s comment doesn’t enumerate individual rapid-growth winners [6]. Industry write-ups and lists spotlighted both “quiet winners” who steadily built revenue and sudden bestsellers who rose through platform mechanics — two different growth profiles with different sustainability risks [6] [5].
6. Limitations and the honest conclusion
Public reporting and third‑party lists provide examples and patterns but do not supply a single, sourced ranking that definitively names the top subscriber-growth winners of 2025; available sources highlight Heather Cox Richardson’s large audience, Jim Acosta and Justin Welsh’s quick paid-user gains, and many newer publications that leapfrogged by importing lists or riding Substack discovery [1] [2] [3] [4]. Without company-published, line-item growth data for 2025, any list of “largest subscriber growth” must be presented as an informed aggregation of reported examples and platform dynamics rather than a definitive numeric ranking.